Objectives. Malrotation of the femoral component can result in post-operative complications in total knee arthroplasty (TKA), including patellar maltracking. Therefore, we used computational simulation to investigate the influence of femoral malrotation on contact stresses on the polyethylene (PE) insert and on the patellar button as well as on the forces on the collateral ligaments. Materials and Methods. Validated finite element (FE) models, for internal and external malrotations from 0° to 10° with regard to the neutral position, were developed to evaluate the effect of malrotation on the femoral component in TKA. Femoral malrotation in TKA on the knee joint was simulated in walking stance-phase gait and squat loading conditions. Results. Contact stress on the medial side of the PE insert increased with internal femoral malrotation and decreased with external femoral malrotation in both stance-phase gait and squat loading conditions. There was an opposite trend in the lateral side of the PE insert case. Contact stress on the patellar button increased with internal femoral malrotation and decreased with external femoral malrotation in both stance-phase gait and squat loading conditions. In particular, contact stress on the patellar button increased by 98% with internal malrotation of 10° in the squat loading condition. The force on the medial collateral ligament (MCL) and the lateral collateral ligament (LCL) increased with internal and external femoral malrotations, respectively. Conclusions. These findings provide support for orthopaedic surgeons to determine a more accurate femoral component alignment in order to reduce post-operative PE problems. Cite this article: K-T. Kang, Y-G. Koh, J. Son, O-R. Kwon, C. Baek, S. H. Jung, K. K. Park. Measuring the effect of femoral malrotation on knee joint biomechanics for total knee arthroplasty using computational simulation. Bone Joint Res 2016;5:552–559. DOI: 10.1302/2046-3758.511.BJR-2016-0107.R1

Purpose. Malrotation of the femur has been documented in as few as 0% and as many as 28% of fractures treated with an intramedullary(IM) nail. Patients with more than 15 degrees of malrotation sometimes require derotation osteotomy. Recognizing malrotation intraoperatively is the most efficient way to avoid corrective surgery. The purpose of this paper is to inform orthopaedic surgeons of the best estimate of incidence of femoral malrotation after IM nailing. This may lead to increased attention toward intraoperative control of malrotation. Method. A literature search was performed by a library sciences professional. Two authors excluded papers not relevant to the study in two stages with clearly outlined criteria and adjudication. Inter-observer agreement was measured with the kappa statistic. Data extraction was performed by the same two authors with measure of agreement and adjudication from a third author. Data extraction included: incidence of malrotation, method used for measurement of malrotation and use of intraoperative techniques to minimize malrotation. Results. Six-hundred-and-seventy-one papers were identified in 3 databases. First stage exclusion based on title and abstract yielded 149 papers. Second stage exclusion based on full text review yielded 51 papers. Inter-observer agreement for exclusion of papers was “very good” (93%, kappa=0.843). The overall incidence of post-traumatic malrotation of the femur after IM nailing was 6%, 95% CI (5%, 8%). The incidence of malrotation identified by clinical examination alone was 3%, 95% CI (2%, 4%), while malrotation diagnosed by radiographic examination (CT, ultrasound and biplanar radiography) was 15%, 95% CI (10%, 20%). If intraoperative techniques to minimize malrotation were applied, incidence decreased to 9%, 95% CI (2%,16%) while without intraoperative attention to rotation, incidence was 19%, 95% CI (13%, 26%). Conclusion. We have found femoral malrotation after IM nailing to be reported in 19% of cases when measured objectively. The present study offers the best available report of incidence for post-traumatic malrotation of the femur by combining all available studies, from Kunchner's initial publication on intramedullary nailing of the femur to date. Jaarsma and Tornetta have reported that clinical examination is poor for detection of malrotation when compared with CT. Our study supports this finding. The quoted incidence for malrotation is consistently lower when measured by clinical examination compared to radiographic measures. This suggests that surgeons under-recognize malrotation intra-operatively, and therefore often fail to correct it. This study has found that any intraoperative effort to minimize rotation decreases its incidence to 9%. It is therefore crucial to have radiographic methods, such as those described by Krettek (lesser trochanter, cortical width and cortical diameter) available for use intra-operatively to diagnose malrotation

INTRODUCTION. It has been reported that the rate of complications around the patella after Total Knee Arthroplasty(TKA) is 1–12%, and the patella dislocation is the most common one. PURPOSE. We will report a case that had the patella dislocation after TKA caused by malrotation of the components. CASE. 67 years old, Female. The chief complaint was an instability of the right patella. She had undergone TKA due to osteoarthritis at another hospital. After 2 months, she felt a subluxation of the patella. And after 4 months, she had a reoperation of medial reefing and revision of the patella at the same hospital, and the doctor allowed her to flex her right knee within 70 degrees. However, after 3 months, she started experiencing pain with a feeling of dislocation and got it corrected and immobilized with a knee brace. 2 weeks later, she visited our hospital for the first time. STATUS. 148cm, 65kg. She could gait with an extension knee brace. Tenderness was seen around the right patella. She could bend her right knee from 0 degrees to 60 degrees. Extension lag and instability of varus and valgus were not existent. An X-ray showed the FTA was 172 degrees on the right side. The right knee had a TKA(Stryker Scorpion Energy®/fixed surface), and the measurements of component after TKA were almost good. However, the patella had lateral subluxation. A CT image showed the femoral component inserted in internal rotation of 8 degrees from CEA and tibia component inserted in internal rotation of 23 degrees from the left Akagi line. We diagnosed right knee dislocation because of rotation failure of the components. COURSE OF TREATMENT. We replaced implants which were produced by the same company. We replaced the tibial component externally referring to the Akagi's line. On the femur side, we augumented the femur component at the posterolateral and replaced it referring to the CEA. We made a lateral release and used a CCK surface. We did not replace the patella because the surviving patella bone was thin and patella tracking was satisfactory.2 weeks after the operation, she could bend her knee from 0 degrees to 120 degrees and walk with a cane. An X-ray showed the patella was reduced and a CT scan showed the appropriate rotation angle. DISCUSSION. Regarding the treatment of patella dislocation after TKA, when there is malrotation of components, revision is recommended. The definition and the degree of malrotation are still controversial. It was reported that when total internal rotation angle was more than 7 degrees, Revision is recommended. This patient obtained the stability of patella due to the proper rotation angle of components

Purpose: Component malrotation is a recognized cause of post total knee arthroplasty (TKA) pain. The objective of this study was to evaluate the functional outcomes of TKA revision for component malrotation, and to compare it to revision surgeries for aseptic loosening as a control comparison group. Method: Twenty four patients who had TKA revision due to component malrotation as the only objective abnormality were reviewed. Only patients with preoperative computerized tomography (CT) documentation of 3° or more malrotation of at least one of the components were included. Mean combined rotation was 6.8° (range, − 12 − 3) excessive internal rotation. Twenty four matched control patients had TKA revision due to aseptic loosening. Results: Mean follow up was 37 months (range, 24–65). Mean interval from index surgery was 41 months (range, 24–65) for the study group and 98 months (range, 11–222) for the control group (p=0.0003). Preoperative Knee Society Score (KSS) improved by 49 points (range, 16–80) at 6 months postoperatively for the malrotation patients and by 39 (range, − 7–78) for the loosening patients (p=0.08). At last follow-up, KSS was 80 (range, 60–89) for the malrotation group and 75 (range, 26–90) for the loosening group (p=0.14). Conclusion: We recommend the use of CT scans in evaluation of all patients with early painful TKA’s and no objective evidence of infection. When component malrotation is demonstrated, we believe the results of this study validate consideration of early revision

Component malrotation in total knee arthroplasty (TKA) is a reason for early failure and revision. Assessment of possible component malrotation using computed tomography (CT) might be useful when other differentials have been excluded. The aims of our study were to determine the proportion of symptomatic patients with component malrotation on CT, and review the subsequent management of such patients. A retrospective review of case notes was performed locally for all patients who had a CT scan for a painful TKA. Measurements of the femoral and tibial component rotations were done according to the standard Berger protocol, giving net degrees of either external rotation (ER) or internal rotation (IR). Any subsequent surgery was noted, and patients were followed up as per local practice. Between 2007 and April 2012, 69 knees in 68 patients had CT scans. There were 25 males and 43 females, and mean age at primary surgery was 65.03 years. The mean femoral component rotation for all knees was 0.1° ER (range 7.0° ER – 6.7° IR), and the mean tibial component rotation for all knees was 19.1° IR (6.6° ER – 37.0° IR). No statistically significant difference was found comparing the mean femoral and tibial component rotations between patients with and without further surgery. Further surgery was performed on 39 (56.5%) knees. Overall, there were ten cases (14.5%) of isolated femoral malrotation, 26 tibial malrotation (37.7%), and two cases (2.9%) had malrotation of both components. Out of these 38 cases, secondary surgery was performed in 22 knees (57.9%), of which a satisfactory outcome was achieved in fifteen cases (68.1%). It is impossible to establish component malrotation as the only cause of pain following TKA, however, our study does show that the Berger protocol has its uses when other causes have been excluded

Purpose of the study: Despite a survival rate to the order of 90–95% at ten years, implant malposition and particularly malrotation can cause an underestimation of failure after total knee arthroplasty (TKA). We report our experience with revision TKA for isolated malrotation. Material and methods: Twelve patients underwent revision for isolated maltrotation of an implant. This series of three men and nine women, mean age 66 years, range 47–74 years at primary surgery, were reviewed retrospectively. During the follow-up, all patients complained of early onset anterior knee pain, which was generally noted severe, associated with moderate patellar instability in four cases, noted severe in 7 others and extreme in one (permanent patellar dislocation). Half of the patients also exhibited hyperlaxity was invalidating instability. Range of motion was generally preserved (2/5/100). In all cases, the rotational problems were confirmed on the computed tomography which revealed predominant tibial malrotation, measured at 23 mean internal rotation and a cumulative malrotation (femur+tibia) of 22 internal rotation. Results: All patients except two required revision of both femoral and tibial implants. In one case, the tibial piece was alone changed and in another, isolated translation of the anterior tibial tuberosity was performed. For eight of eleven cases, the revision implants had a stem and femoral inserts were used to control the bone stock loss induced by the corrective cuts in six cases and requiring more or less extensive ligament balance procedures in six. At mean follow-up (30 months, range 12–60), there was a very significant improvement in the functional results; only one patients with a history of patellectomy complained of persistent anterior pain. None of the patients complained of patellar instability. Discussion: Excessive cumulative internal rotation of the implants induces increased stress on the patella, causing early anterior pain, then subluxation and finally dislocation beyond −15 to −20° internal rotation. These position errors are concentrated on the tibia were care must be taken to respect the anatomic landmarks (bicondylar axis, anterior tibial tuberosity) to avoid early failure. In the event of major rotational disorders, revision may be required with procedures to correct the ligament balance

Aims: In this prospective study, we determined whether corrective surgery for rotational malalignment of femoral prosthesis components would benefit patients that had previously undergone total knee arthroplasty. Methods: 68 consecutive patients with a painful total knee arthroplasty were screened with computed tomography. All patients were offered plain radiographs, tangential radiographs and stress radiography for valgus/varus stability in 20° and 90° flexion. No patient had signs of infection or loosening. 14 patients were selected that had isolated internal malrotation of the femoral component. No other malpositions could be found. Two patients with mild (≤3°) internal mal-rotation were excluded due to conservative treatment. Revision surgery was performed to replace prosthetic components in 12 patients with internal malrotation ≥ 4° within 3 years of the primary arthroplasty. Results: The corrective surgery resulted in an increase in the average Knee Society Score from 51/65 to 86/86 points and an improvement in the average Hospital for Special Surgery knee score from 64 to 83 points. The mean follow-up was 57 (range 46 to 89) months. Conclusion: This study showed that correction of isolated internal malrotation of the femoral component will lead to better clinical and functional outcomes

Introduction: Stiffness after primary total knee arthroplasty (TKA) is a severe complication that has been associated with excessive internal rotation of the femoral component. Methods: Between 2001 and 2004, 18 patients with 18 well-fixed, aseptic primary TKA underwent revision TKA at a single high-volume joint replacement center for stiffness in the presence of femoral component mal-rotation. Stiffness was defined as ROM with less than 90° of maximum flexion or a flexion contracture greater than 10°. Femoral component malrotation was defined as a condylar twist angle of more than 4° of internal rotation using CT scans. Following IRB approval, 17 out of 18 patients (median age at time of the index surgery 62.7 years, range 45 to 78; female, n=11; male, n=6) were available for retrospective outcome assessment. The mean time between primary and revision TKA was 3.2 years (range, 9–79 months). At a mean follow-up of 3.3 years (range, 2 to 6), all patients were evaluated clinically using the Knee Society objective and functional scores, and by CT measurement of femoral component rotation. Patients without additional procedures between primary and index revision TKA (group A, n=9) were compared using Student t-testing with those which had undergone additional interventions (group B, n=8). Results: Five patients had required additional procedures after the index revision TKA including closed manipulation under anesthesia in one case, patellar resurfacing in one case, metal removal after tubercle osteotomy and open debridement in another case, and tibial component revision followed by revision TKA in one case. CT scans after revision TKA revealed correction of femoral component rotation in all but one case from each group. After revision TKA, the mean objective score was overall 73 points, in group A 82 points compared to 63 points in group B (p< 0.001). In group A there were 78% excellent or good results compared to 13% in group B. The mean function score was overall 74 points, 78 points in group A compared to 69 points in group B. There were 67% good or excellent results in group A compared to 12% in group B. Mean flex-ion increased overall from 71 to 92 degrees (p< 0.01), in group A from 61 to 96 degrees (p< 0.01) and in group B from 82 to 89 degrees. Mean flexion contracture was reduced overall from 7 to 4 degrees, in group A from 6 to 3 degrees, and in group B from 8 to 5 degrees. Stiffness persisted in four cases (24%) (group A, n=1; group B, n=3). Satisfaction (VAS 0–100; 100=completely satis-fied) scored overall a mean of 52 points, in group A 57 points and in group B 44 points. Conclusion: Overall, revision TKA for knee stiffness associated with femoral component internal malrotation resulted in significantly improved knee motion. However, outcome was less predictable in those patients with additional procedures between primary and revision TKA

Introduction: Malrotations following Several complications have been reported in femoral nailing, among them. The aim of this study is to develop an intraoperative method based on cone beam CT (CBCT) to assess comminuted fracture periaxial rotation. We hypothesize that bone surface matching using CBCT image data can precisely predict malrotation in the fractured femur even with severe comminution. Methods: A mid-shaft osteotomy in a fresh frozen cadaveric femur was performed and a rotational axis was formed. The proximal part of the femur was fixed and the distal part was optically racked for periaxial rotation. At each rotation a CBCT was aquired. The images were segmented at bone threshold. The center of the bone in each axial slice was calculated and the distance from that center to the inner and outer bone surfaces was sampled at 1o intervals (360x). The resulting plot was an unwrapped virtual bone surface consisting of a pattern of ridges and valleys. Fracture gaps were simulated by removing CT slices adjacent to the osteotomy. The fracture gap was reconstituted using an extrapolation algorithm to the midline of the fracture. The two bone surfaces were then continuously shifted relative to one another in order to match the geometric bony features. Calculated malalignments were compared to the measured at each of the 16 rotations with each of the 9 simulated fracture gaps. Three rotational malrotations were tested twice to assess repeatability. Results: Femoral malrotation was strongly predicted as compared to the rotation measured by optical tracking. The performance was not impacted by gap size up to 100 mm. Discussion: The high quality of intraoperative CBCT imaging data enables surface matching algorithms to be utilized. The results ratify this novel method for assessing fracture rotation

Introduction. Malrotation of the femoral component is a cause of patellofemoral maltracking after TKA. Its precise effect on the patellofemoral (PF) mechanics has not been well quantified. The aim of this study was to investigate the effect of malrotation of the femoral component on PF initial contact area, initial contact pressure and wear after 4 million full gait cycles in TKA using a knee simulator. Moreover, the influence of the counterface material (CoCr or OxZr) on PF wear was also investigated. Materials & Methods. Femoral components (FCs) were cemented onto specially designed fixtures, allowing positioning of the FC in different angles of axial rotation. Patellar buttons and FCs were then mounted in a Prosim knee simulator. Patellofemoral contact mechanics. Seven axial rotation configurations were tested: neutral (FC parallel to the epicondylar axis), 2.5° endo- and exorotation, 5° endo- and exorotation and 7.5° endo- and exorotation. Patellar contact location, contact area and contact pressure were measured dynamically during 20 gait cycles with a Tekscan sensor covering the patella collecting data at a rate of 100 frames per second. Patellofemoral wear. For three alignments (neutral, 5° endo- and exorotation), a PF wear test of 4 million cycles in bovine serum (diluted to 40%) was done with three CoCr and three OxZr components on conventional ultra-high molecular weight polyethylene (UHMWPE, density: 0.93mg/mm. 3. ). Every 0.5 million cycles the test lubricant was replaced, the patellar samples were cleaned and dried and polyethylene wear was measured gravimetrically. A linear regression model was used to calculate the wear rate of each patellar sample. Aggregate wear rates were determined for each test condition by pooling the measurements of all three patellar samples. Results. For all six endorotation and exorotation configurations, the contact area was significantly lower and the contact pressure significantly higher than the neutral position (p < 0.001, Figs 1 and 2). In the patellofemoral wear test, the highest average wear rate was found in the group of endorotated CoCr femoral components (0.54 mm. 3. /Mcycle), but this is still only 11% of a typical tibiofemoral wear rate with the same CoCr component (5 mm. 3. /Mcycle). The following trends in the average wear rates could be observed: the average wear rate for CoCr (0.34 mm. 3. /Mcycle) was higher than for OxZr (0.19 mm. 3. /Mcycle) and the average wear rate for 5° endorotation (0.35 mm. 3. /Mcycle) was higher than for 5° exorotation (0.21 mm. 3. /Mcycle) and neutral alignment (0.23 mm. 3. /Mcycle) (Figs 3 and 4). None of these differences reached statistical significance (p=0.05), though. Discussion. Our results indicate that both internally and externally malrotated femoral components significantly decrease contact areas and significantly increase contact pressures in the patellofemoral joint. These significant changes in contact pressure didn't translate in significant changes in wear, however. Overall, patellofemoral wear is very small compared to tibiofemoral wear, in all the configurations that we investigated. Based on our results, we can conclude that clinical problems with patellar maltracking after femoral component malrotation seem not to be related to increased wear, but rather to pain and patellar instability

Purpose. Unicompartmental knee replacement (UKR) is an established, bone preserving surgical treatment option for medial compartment osteoarthritis (OA). Early revision rates appear consistently higher than those of total knee replacement (TKR) in many case series and consistently in national registry data. Failure with progression of OA in the lateral compartment has been attributed, in part, to surgical technical errors. In this study we used navigation assisted surgery to investigate the effects of improper sizing of the mobile bearing and malrotation of the tibial component on alignment and lateral compartment loading. Method. A total of eight fresh frozen cadaveric lower limbs were used in the study. After thawing overnight, a Brainlab navigation system with an Oxford (Biomet, Inc) medial UKR module was used to capture the native knee anatomy and alignment using a digitizing probe. Following registration, the case was performed with navigation verified neutral cuts and an ideal insert size was selected to serve as a baseline. The bearing thickness was subsequently increased by 2 mm increments to simulate progressive medial joint overstuffing. Excessive tibial internal rotation of 12 was also simulated at each of the intervals. Knee alignment in varus or valgus was recorded in real time for each surgical scenario with the knee in full extension and at 20 of flexion. Lateral compartment peak pressure was measured using a Tekscan pressure map. Results. Incremental overstuffing of the medial compartment with inserts of increasing thickness resulted in a progressive shift to more valgus knee alignment. Internally rotated sagittal cuts at 12 resulted in a further valgus shift for a given insert size. The valgus shift was detectable at full extension however it was more pronounced at 20 of flexion. Conclusion. The intentional technical errors of overstuffing and malrotation in UKR produced coronal valgus knee alignment and a greater load shift to the lateral compartment. These errors can be construed to contribute to the higher early failure rates associated with UKR when compared to TKR. Special care should be taken to ensure a neutral sagittal tibia cut and appropriate bearing selection. The Intra operative verification of knee alignment should be conducted at 20 of flexion where such errors will be easier for the surgeon to detect and rectify

Aims: To evaluate the clinical signiþcance of isolated femoral malrotation after otherwise well performed painful TKAñs. Methods: 11 painful TKAñs (5 female, 6 male, mean 61 years, range 41 to 73) with normal mechanical axis, patella tracking, stability in extension and no signs of infection or loosening were included in this prospective study. The knees were evaluated by routine clinical and radiographic examinations in combination with a standardized computer tomography (CT) to measure the rotation of the components, using the transepicondylar axis as a reference for the femur. Results: All patients had progressive persistent pain from the time of surgery which was resistant to conservative therapy. There were two groups according to the clinical symptoms: limited ßexion and medial pain at the proximal tibia (4) or ßexion > 90û with anterior knee pain during stairs descending or raising from a chair (7). Standard x-rays were normal but in the special CT all patients showed isolated internal malrotation of the femoral component mean 7û (2 to 10). 9 patients required revision surgery with correction of the malrotated femoral component. The two patients who did not want revision surgery had only minor malrotation (< 4û).Conclusions: In painful TKAñs with unknown persistent pain but limited ßexion and/or lateral instability in the ßexion gap evaluation of the femoral component rotation with a special CT should be performed

Introduction. Malpositioning of the tibial component is a common error in TKR. In theory, placement of the tibial tray could be improved by optimization of its design to more closely match anatomic features of the proximal tibia with the motion axis of the knee joint. However, the inherent variability of tibial anatomy and the size increments required for a non-custom implant system may lead to minimal benefit, despite the increased cost and size of inventory. This study was undertaken to test the hypotheses: . 1. That correct placement of the tibial component is influenced by the design of the implant. 2. The operative experience of the surgeon influences the likelihood of correct placement of contemporary designs of tibial trays. Materials and Methods. CAD models were generated of all sizes of 7 widely used designs of tibial trays, including symmetric (4) and asymmetric (3) designs. Solid models of 10 tibias were selected from a large anatomic collection and verified to ensure that they encompassed the anatomic range of shapes and sizes of Caucasian tibias. Each computer model was resected perpendicular to the canal axis with a posterior slope of 5 degrees at a depth of 5 mm distal to the medial plateau. Fifteen joint surgeons and fourteen experienced trainees individually determined the ideal size and placement of each tray on each resected tibia, corresponding to a total of 2030 implantations. For each implantation we calculated: (i) the rotational alignment of the tray; (ii) its coverage of the resected bony surface, and (iii) the extent of any overhang of the tray beyond the cortical boundary. Differences in the parameters defining the implantations of the surgeons and trainees were evaluated statistically. Results. On average, the tibial tray was placed in 5.5 ± 3.1° of external rotation. The overall incidence of internal rotation was only 4.8%: 10.5% of trainee cases vs. 0.7% of surgeon cases (p < 0.0001). The incidence of internal rotation varied significantly with implant design, ranging from 1.7% to 6.2%. Bony coverage averaged 76.0 ± 4.5%, and was less than 70% in 8.6% of cases. Tibial coverage also varied significantly between designs (73.2 ± 4.3% to 79.2 ± 3.8%; p < .0001). Clinically significant cortical overhang (>1 mm), primarily in the posterior-lateral region, was present in 12.1% of cases, and varied by design, as expressed by the area of the tray overhanging the cortical boundary (min: 2.3 ± 6.7 mm. 2. ; max: 4.7 ± 7.9 mm. 2. ; p < .0001). The surgeons and the trainees also differed in terms of the incidence of sub-optimal tibial coverage (10.0% vs. 14.4%, p < 0.001), and cortical overhang (7.4% vs. 9.7%, p < 0.001). Discussion. 1. Malrotation, bony coverage and cortical overhang are all strongly influenced by the design of the tibial tray selected and the experience of the surgeon. 2. Compared to trainees, experienced surgeons tend to position tibial trays in more external rotation, and with less concern for reduced bony coverage and cortical overhang than trainees. 3. This study supports the hypothesis that improvements in the outcome and reliability of TKR may be achieved through attention to implant design

The aim of this study is to identify the incidence of mal-rotation of TKR components in a group of patients with unexplained knee pain identified from the University of Dundee joint replacement database and compare that group with a group of painless TKRs. 38 of 45 NexGen LPS Total Knee Replacements identified with unexplained pain at a minimum of 1 year following surgery underwent CT scanning to determine rotational alignment. All patients had a Knee Society Pain score of 20 points or less and a mean Visual Analogue Pain Score of greater than 4.0. This group was compared with a control group of 26 TKRs all of which had never reported pain from 1 year post surgery. In the painful group mean femoral component rotation was 2.2° of internal rotation (range 8.8°IR to 3.9°ER, sd 3.6, SEm 0.59) compared to 0.9°IR (range 6.9°IR to 6.8°ER, sd 3.39, SEm 0.67) in the painless group (p= 0.15). In the painful group 21.6% of femoral components were more than 6° internally rotated compared with 7.7% in the painless group however this was not statistically significant (p=0.18). No femoral components in either group were in excessive (over 8 degrees) ER. Tibial component rotation was much more variable than femoral component rotation in both groups particularly in the painful group. Mean tibial component rotation was 4.1°IR (range 37.9°IR to 31.1°ER, sd 14.6, SEm 2.4) in the painful group compared to 2.2°ER (range 8.5°IR to 18.2°ER, sd 6.95, SEm 1.36) in the painless group (p=0.024). 15 tibial components (39.5%) were greater than 10° internally rotated in the painful group whilst no tibial components were more than 10° internally rotated in the pain free group (p< 0.001). In the painful group 7 tibial components (18.4%) were more than 10° externally rotated whilst 4 (15.4%) were in more than 10° ER in the painless group (p=1.00). Overall 22 tibial components (57.9%) were in more than 10° of malrotation in the painful group compared with 4 (15.4%) in the pain free group (p=0.05). Mean rotational mismatch between femoral and tibial components was 1.9° tibial IR (range 39.7° tibial IR to 35.1° tibial ER, sd 16.1, SEm 2.7) in the painful group whilst in the painless group mean rotational mismatch was 3.1 degrees tibial ER (range 10.3° tibial IR to 22.1° tibial ER, sd 8.4, SEm 1.65). This difference was not significant (p=0.12). 16 TKRs (55.3%) had rotational mismatch of more than 10° in the painful group compared to 7 (26.9%) in the control group (p=0.02). We conclude that rotational malalignment is frequent in painful total knee replacements and may be a major cause of pain after TKR. In particular tibial internal rotation is the most frequent alignment error in the painful TKR and appears to play a major role in the aetiology of pain after TKR

Introduction

Stiffness postTotal Knee Replacement (TKR) is a common, complex and multifactorial problem. Many reports claim that component mal-rotation plays an important role in this problem. Internal mal-rotation of the tibial component is underestimated among surgeons when compared to femoral internal mal-rotation. We believe the internal mal- rotation of thetibial component can negatively affect the full extension of Knee. We performed an in-vivo study of the impact of tibial internal mal-rotation on knee extension in 31 cases.

In TKA, prosthetic femoral and tibial implants must be symmetrically placed and matched in the mechanical axis and the ligament gaps must be correctly balanced. The collateral ligaments are the key guide, as they arise from the epicondyles of the distal femur, are perpendicular to the AP axis of Whiteside, and are coincident with the transtibial axis of the proximal tibial surface. A perpendicular bisection of the transtibial axis creates the AP axis of the tibia which is coincident in space with the AP axis of Whiteside (Berger). Measured distal femoral resection targets including TEA, AP axis of Whiteside, and 3 degrees external to the posterior condylar axis works because the stout posterior cruciate ligament limits laxity in flexion, allowing for the anatomical variation of these landmarks to be accommodated. The Insall, Ranawat gap balancing methods work to balance the knee in flexion, often matching the results of a measured resection, but guaranteeing a symmetrically balanced flexion gap. Distal femoral internal rotation can result if the medial collateral is over-released, but experience has shown this not to be a problem if the gaps are well balanced. Tibial tray position must be placed coincident with the AP axis of the tibia, which also is coincident with Akagi's line (line from medial margin of patellar tendon to center of the posterior cruciate ligament). The surgeon can make a line from the AP axis of Whiteside to the anterior tibial which matches the AP tibial axis.

Introduction

Stiffness post Total Knee Replacement (TKR) is a common, complex and multifactorial problem. Many reports claim that component mal-rotation plays an important role in this problem. Internal mal-rotation of the tibial component is underestimated among surgeons when compared to femoral internal mal-rotation. We believe the internal mal-rotation of the tibial component can negatively affect the full extension of Knee. We performed an in-vivo study of the impact of tibial internal mal-rotation on knee extension in 31 cases.

The purpose of this study was to determine whether internal mal-rotation of the femoral component is associated with arthrofibrosis in TKA. Multiple etiological factors have been suggested, but specific causes have not been identified. We hypothesized arthrofibrosis may be triggered by a combination of non-physiological kinematics (femoral component internal rotation) and a tight medial compartment.

From a consecutive cohort of 3058 mobile bearing TKA forty-four (1.4%) cases were diagnosed as having arthrofibrosis, of which thirty-eight (86%) cases could be recruited. Thirty-eight patients with a well functioning TKA served as matched controls. Evaluation included CT investigation to determine femoral component rotation with reference to the transepicondylar axis (TEA).

Results: Femoral components in the AF group were significantly (p< 0.00001) internally mal-rotated by a mean of 4.7 degrees ranging from ten degrees internal rotation (IR) to one degree external rotation (ER). Mean femoral rotational in the control group was parallel (0.3 degrees IR) to the TEA (six degrees IR to four degrees ER). Arthrofibrosis was not associated with age, gender, body-mass-index, or preoperative diagnosis

There is a highly significant association between arthrofibrosis in TKA and internal mal-rotation of the femoral component. On the base of these results it was hypothesized that non-physiological kinematics in TKA with mal-aligned femoral components influence and/or trigger arthrofibrosis in TKA.

Aims. The material and design of knee components can have a considerable effect on the contact characteristics of the tibial post. This study aimed to analyze the stress distribution on the tibial post when using different grades of polyethylene for the tibial inserts. In addition, the contact properties of fixed-bearing and mobile-bearing inserts were evaluated. Methods. Three different grades of polyethylene were compared in this study; conventional ultra high molecular weight polyethylene (UHMWPE), highly cross-linked polyethylene (HXLPE), and vitamin E-stabilized polyethylene (VEPE). In addition, tibial baseplates with a fixed-bearing and a mobile-bearing insert were evaluated to understand differences in the contact properties. The inserts were implanted in neutral alignment and with a 10° internal malrotation. The contact stress, von Mises stress, and equivalent plastic strain (PEEQ) on the tibial posts were extracted for comparison. Results. The stress and strain on the tibial post for the three polyethylenes greatly increased when the insert was placed in malrotation, showing a 38% to 56% increase in von Mises stress and a 335% to 434% increase in PEEQ. The VEPE insert had the lowest PEEQ among the three materials. The mobile-bearing design exhibited a lower increase in stress and strain around the tibial posts than the fixed-bearing design. Conclusion. Using VEPE for the tibial component potentially eliminates the risk of material permanent deformation. The mobile-bearing insert can help to avoid a dramatic increase in plastic strain around the tibial post in cases of malrotation. The mobility allows the pressure to be distributed on the tibial post and demonstrated lower stresses with all three polyethylenes simulated. Cite this article: Bone Joint Res 2020;9(11):768–777

Aims. Traditionally, total hip arthroplasty (THA) templating has been performed on anteroposterior (AP) pelvis radiographs. Recently, additional AP hip radiographs have been recommended for accurate measurement of the femoral offset (FO). To verify this claim, this study aimed to establish quantitative data of the measurement error of the FO in relation to leg position and X-ray source position using a newly developed geometric model and clinical data. Methods. We analyzed the FOs measured on AP hip and pelvis radiographs in a prospective consecutive series of 55 patients undergoing unilateral primary THA for hip osteoarthritis. To determine sample size, a power analysis was performed. Patients’ position and X-ray beam setting followed a standardized protocol to achieve reproducible projections. All images were calibrated with the KingMark calibration system. In addition, a geometric model was created to evaluate both the effects of leg position (rotation and abduction/adduction) and the effects of X-ray source position on FO measurement. Results. The mean FOs measured on AP hip and pelvis radiographs were 38.0 mm (SD 6.4) and 36.6 mm (SD 6.3) (p < 0.001), respectively. Radiological view had a smaller effect on FO measurement than inaccurate leg positioning. The model showed a non-linear relationship between projected FO and femoral neck orientation; at 30° external neck rotation (with reference to the detector plane), a true FO of 40 mm was underestimated by up to 20% (7.8 mm). With a neutral to mild external neck rotation (≤ 15°), the underestimation was less than 7% (2.7 mm). The effect of abduction and adduction was negligible. Conclusion. For routine THA templating, an AP pelvis radiograph remains the gold standard. Only patients with femoral neck malrotation > 15° on the AP pelvis view, e.g. due to external rotation contracture, should receive further imaging. Options include an additional AP hip view with elevation of the entire affected hip to align the femoral neck more parallel to the detector, or a CT scan in more severe cases. Cite this article: Bone Jt Open 2022;3(10):795–803