Background. The decision to resurface the patella during total knee arthroplasty remains controversial. Aim of our study was to evaluate the functional difference between patients undergoing medial rotation knee (MRK) replacement with and without patellar resurfacing at our hospital. Methods. We did a retrospective analysis of patients undergoing MRK total knee replacement (Matortho) at our hospital between 2008 and 2017 performed by 2 surgeons. Patients were recalled for a clinical review from Oct 2017 for recording of Oxford knee, Baldini and Ferrel scores. Mann-Whitney U test was used for non-parametric data (SPSS v24). Results. Of the 104(49 males) patients, 62 had patellar resurfacing. Age and sex distribution was similar in both groups. The mean follow up period was 74.45 months in non- resurfaced group and 54.93 months in resurfaced group. The Median (Range) pre-operative Oxford knee scores were similar in both groups − 15(4–42) in non-resurfaced group and 14(1–44) in resurfaced group. The median OKS at follow-up were 36(12–47) in non-resurfaced group and 37(9–48) in resurfaced group. The Patellar scores were slightly better in the resurfaced group – Baldini score median (range) (90 (25–100) in non resurfaced v/s 100(30–100) in resurfaced), Ferrel score (median (range) 25(12–30) in non-resurfaced v/s 28(10–30) in resurfaced, p 0.042). The patellofemoral component of the OKS (Q5 + Q7 + Q12) median (range) showed an improvement from 3(1–11) to 6.5 (3–11) in non-resurfaced group and from 3(0–12) to 8 (2–12) (p 0.039) in resurfaced group. Conclusion. Although the overall functional knee scores in non-resurfaced and resurfaced groups were same, we found a statistically significant difference in Ferrel score and in the patellofemoral component of OKS between the 2 groups of MRK knee replacement suggesting specific benefits of patellar resurfacing

The performance of total knee arthroplasty in deeply flexed postures is of increasing concern as the procedure is performed on younger, more physically active and more culturally diverse populations. Several implant design factors, including tibiofemoral conformity, tibial slope and posterior condylar geometry have been shown directly to affect deep flexion performance. The goal of this study was to evaluate the performance of a fixed-bearing, asymmetric, medial rotation arthroplasty design during kneeling activities. Thirteen study participants (15 knees) with primary total knee arthroplasty (Medial Rotation Knee, Finsbury, Surrey, UK) were observed while doing a step activity and kneeling on a padded bench from 90° to maximum comfortable flexion using lateral fluoroscopy. Subjects averaged 74 years of age and nine were female. Subjects were an average of 17 months post-operative, and scored 94 points on the International Knee Score and 99 on the Functional Score. Digitised fluoroscopic images were corrected for geometric distortion and 3D models of the implant components were registered to determine the 3D position and orientation of the implants in each image. During the step activity, the medial and the lateral femoral contact point stayed fairly constant with no axial rotation from 0 to 100° of flexion. At maximum kneeling flexion, the knees exhibited 119° of implant flexion (101°-139°), 7° (-7° to 17°) tibial internal rotation, and the lateral condyle translated backwards by 11 mm. Patients with medial rotation knee arthroplasty exhibited medial pivot action with no paradoxical translation. The knees exhibited excellent kneeling flexion and posterior translation of the femur with respect to the tibia. The axial rotation in MRK was within the range of normal knee kinematics from -10 to 120 (perhaps 140)

Purpose. To report clinical results and demonstrate any posterior femoral translation (PFT) in medial rotation total knee arthroplasty (TKA) of posterior cruciate ligament (PCL) retaining type. Materials and Methods. A prospective study was performed upon thirty consecutive subjects who were operated on with medial rotation TKA of PCL retaining type (Advance® Medial Pivot prosthesis with ‘Double High’ insert; Wright Medical Technology, Arlington, TN, USA) (Fig. 1). between March 2009 and March 2010 and had been followed up for a least 2 years. Inclusion criteria were age between 60 and 75 years and primary degenerative joint disease of knee graded as Kellgren Lawrence grade III or higher. Exclusion criteria were age under 60 years, any inflammatory joint disease including rheumatoid arthritis, early stage of primary degenerative joint disease of knee or any history of previous osteotomy around knee. Clinically, the knee society knee score and function score were used to evaluate pain and function. At last follow-up, all subjects performed full extension, thirty degree flexion and full active flexion sequentially under fluoroscopic surveillance. In each of these lateral radiographs, anteroposterior(AP) condylar position was pinpointed and the magnitude of PFT was determined by degree of transition of AP condylar position from full extension to full active flexion radiograph (Fig. 2 A–B). Statistical methods used were paired t-test, Pearson correlation, Steadman rank correlation and regression analysis. Component migration and radiolucent line were also observed. Results. At last follow-up, the mean knee society knee score and the mean function score improved significantly compared to preoperative scores (from 61.5 to 90.4 and from 57.8 to 84.7 respectively). The mean maximum flexion of knee increased postoperatively compared to preoperative one without any significant difference (105.5Ëš±11.2Ëšvs 109.3Ëš±9.8Ëš, p=0.051, β=0.387). Neverthless, regression analysis showed a good linear association (r = 0.53, p=0.0027) between the pre- and post-operative maximum flexions of knee. The AP condylar positions were consistently posterior to midline throughout the entire range of flexion. The mean maximum PFT was 10.5 mm (± 4.3 mm) and the magnitude of maximum PFT was greater in higher flexion cases (r = 0.57, p = 0.0009) (Fig. 3). There were no cases having either component migration or radiolucent line except for one case showing instability related to trauma. Conclusions. In medial rotation total knee arthroplasty of PCL retaining type, clinical outcomes were satisfactory and the maximum obtainable flexions tended to be in narrower ranges than those of preoperative ones and smaller than those of other TKA prostheses. Nonetheless, reliable posterior femoral translations were observed during progressive flexions of knees, which was considered to be one of important kinematic factors in increasing the level of knee flexion of medial-rotation TKA in longer follow-ups by providing greater posterior clearance and reduced femoro-tibial impingement

Background. In the late 1980's Michael Freeman conceived the idea that knee replacement would most closely replicate the natural knee joint, if the medial Tibio-Femoral articulation was configured as a “ball-in-socket”. Over the last three decades, medial rotation and medial pivot designs have proved successful in clinical use. Freeman's final iteration of the medial ball-in-socket concept was the Medial Sphere knee. We report the three-year survivorship, clinical outcomes, patient reported outcome measures (PROMs) and radiographic analysis of this implant in a multi-centre, multi-surgeon, prospective observational study. Methods. Patients awaiting total knee replacement were recruited by four centres. They had no medical contraindication to surgery, were able to provide informed consent and were available for follow-up. Primary outcome was implant survival at six months, one, two, three and five years. Secondary outcomes were patient reported outcome measures: Oxford Knee Score (OKS), Euroqol (EQ-5D), International Knee Society Score (IKSS), IKSS Functional score and Health State score, complications and radiographic outcomes. Radiographic analysis was undertaken using the TraumaCad software and data analysis was undertaken using SPSS. Results. To date, 328 female and 202 male patients with a mean age 66.9 years and mean body mass index 30.0 were recruited. Three year Kaplan-Meier survivorship analysis of cumulative failure showed an implant survival of 99.46% (95% confidence interval 100 – 96.74), when deaths and withdrawals were treated as censored data. Twelve patients withdrew (2.26%), seven died (1.32%) and two knees were revised (0.38%). The mean EQ5D, Health State Scores, OKS, IKSS & IKSS Function scores at three years improved significantly from pre- operative scores (Health State Score: 9.91 (65.59 pre-op to 75.50); OKS: 18.82 (19.90 pre-op to 38.72); IKSS: 39.87 (44.39 pre-op to 92.09); IKSS Function Score: 35.03 (49.42 pre-op to 84.45). The mean improvement of EQ5D at three years was: 0.34 (0.48 pre-op to 0.82). Discussion. Survival of the GMK Sphere to three years in this study was over 99%. Risk of revision compares favourably with UK National Joint Registry (NJR) data. The improvements that are seen in patient reported outcome measures reflect an enhancement in patient function and quality of life. Conclusion. At three years follow-up, the implant demonstrates satisfactory survival and outcomes. Patient matching and evaluation of more cases, at more time points will allow outcome comparison with other implant options

Introduction. Natural population variation in femoral morphology results in a large range of offsets, anteversion angles and lengths. During total hip arthroplasty, accurate restoration of hip biomechanics is essential to achieve good functional results. One option is to restore the anatomic hip rotation center. Alternatively, medializing the rotation center and compensating by increasing the femoral offset, reduces acetabular contact forces and increases the abductor lever arm. We investigated the ability of two cemented stem systems to restore hip biomechanics in an anatomic and medialized way. We compared an undersized “Exeter-type” of stem with three offset options and 18 sizes (CPT, Zimmer), to a line-to-line “Kerboul-type” of stem with proportional offset and 12 sizes (Centris, Mathys). Methods. Thirty CT scans of whole femora were segmented and the hip rotation center, proximal femoral axis and femoral length were determined with Mimics and 3-matic (Materialise). Using scripting functionality in the software, CAD design files of both stems were automatically sized and aligned along the proximal femoral axis to restore an anatomical and a 5 mm medialized hip rotation center. Stem size and position could be fine-tuned manually. The maximum distances between the prosthetic (PRC), the anatomic (ARC) and the medialized hip rotation center (MRC) were calculated (Fig. 1). Variations in femoral offset (ΔFO), anteroposterior (ΔAP) and proximodistal distance (ΔPD) were analyzed. Finally, the number of cases where the hip rotation center could be restored within 5 mm was reported. Results. Both implants allowed restoring the ARC accurately (mean distance PRC-ARC: CPT 0.97±0.88 mm, Centris 1.66±1.59 mm; mean difference ΔFO: CPT 0.09±0.19 mm, Centris 0.11±0.29 mm; mean difference ΔAP: CPT 0.12±1.22°, Centris 0.27±1.78 mm, mean difference ΔPD: CPT 0.04±0.44 mm, Centris 0.49±1.35 mm). The CPT stem allowed restoring the PRC within 5 mm of the ARC in all cases (max. 4.31 mm), whereas the Centris stem achieved this in only 28/30 hips (max. 6.72 mm) (Fig. 2). Aiming for a MRC was less satisfactory with both stems (mean distance PRC-MRC: CPT 1.38±1.63 mm, Centris 3.61±2.73 mm; mean difference ΔFO: CPT 0.09±0.10 mm, Centris 0.06±0.35 mm; mean difference ΔAP: CPT 0.17±2.02 mm, Centris 2.58±2.68 mm, mean difference ΔDP; CPT 0.28±0.67 mm, Centris 1.98±1.66 mm). The CPT stem allowed restoring the PRC within 5 mm of the MRC in 29/30 cases (max. 8.09 mm), whereas the Centris stem achieved this in only 25/30 cases (max. 11.15 mm) (Fig. 3). Discussion. Although both stem systems allowed restoring hip biomechanics accurately in most cases, the CPT system was superior to the Centris stem for achieving both ARC and MRC. This could be explained by more implant sizes (18 vs. 12) and undersized stems offering more freedom to correct version. Although medializing the hip rotation center offers biomechanical advantages, both stems had more difficulties achieving this. In some cases, differences between aimed and planned rotation centers were close to 1 cm which might negatively impact on clinical outcome. As such, to avoid suboptimal reconstructions with the available implants, templating is mandatory especially when aiming at a medialized reconstruction strategy

INTRODUCTION. In native knees anterior cruciate ligament (ACL) and asymmetric shape of the tibial articular surface with a convex lateral plateau are responsible for differential medial and lateral femoral rollback. Contemporary ACL retaining total knee arthroplasty (TKA) improves knee function over ACL sacrificing (CR) TKA; however, these implants do not restore the asymmetric tibial articular geometry. This may explain why ACL retention addresses paradoxical anterior sliding seen in CR TKA, but does not fully restore medial pivot motion. To address this, an ACL retaining biomimetic implant, was designed by moving the femoral component through healthy in vivo kinematics obtained from bi-planar fluoroscopy and sequentially removing material from a tibial template. We hypothesized that the biomimetic articular surface together with ACL preservation would better restore activity dependent kinematics of normal knees, than ACL retention alone. METHODS. Kinematic performance of the biomimetic BCR design (asymmetric tibia with convex lateral surface), a contemporary BCR implant (symmetric shallow dished tibia) and a contemporary CR implant (symmetric dished tibia) was analyzed using KneeSIM software. Chair-sit, deep knee bend, and walking were analyzed. Components were mounted on an average bone model created from magnetic resonance imaging (MRI) data of 40 normal knees. Soft-tissue insertions were defined on the average knee model based on MRI data, and mechanical properties were obtained from literature. Femoral condyle center motions relative to the tibia were tracked to compare different implant designs. RESULTS. During simulated chair-sit, the biomimetic BCR implant showed knee motion similar to that reported for healthy knees in vivo including medial pivot rotation with greater rollback of the lateral femoral condyle (5 mm medial vs. 11 mm lateral). The CR implant showed posterior femoral subluxation in extension, paradoxical anterior sliding until 60° flexion followed by limited rollback until 105° with no medial pivot rotation. The conventional BCR implant reduced initial posterior shift of the femur in extension, however, medial pivot rotation and steady posterior rollback was not achieved. Similar trends were also found for deep knee bend activity. During walking the CR implant showed posterior subluxation in extension followed by anterior motion similar to the chair-sit activity. Both BCR implants showed less femoral excursion without posterior subluxation similar to published in vivo kinematics data for bi-uni patients. CONCLUSION. By simulating a variety of daily activities with different ranges of knee motion we were able to show that the ACL preserving biomimetic TKA implant could restore activity dependent normal knee kinematics unlike contemporary ACL retaining and ACL sacrificing implants. For chair-sit activity there was a clear medial pivot pattern for the biomimetic BCR design (unlike any other implant), while for lower flexion activities there was no medial pivot apparent in our simulations. These activity dependent knee motions are consistent with published in vivo kinematics and confirmed our hypothesis that biomimetic articular surface together with ACL preservation may be required to restore normal knee function. The biomimetic BCR design with its anatomical articular surface together with ACL preservation may provide patients with a more normal feeling knee following TKA surgery

INTRODUCTION. ACL retaining (BCR) Total Knee Arthroplasty (TKA) provides more normal kinematics than ACL sacrificing (CR) TKA. However, in the native knee the ACL and the asymmetric shape of the tibial articular surface with a convex lateral plateau are responsible for the differential medial/lateral femoral rollback (medial pivot). Therefore, the hypothesis of this study was that an asymmetric biomimetic articular surface together with ACL preservation would better restore native knee kinematics than retention of the ACL alone. Normal knee kinematics from bi-planar fluoroscopy was used to reverse engineer the tibial articular surface of the biomimetic implant. This was achieved by moving the femoral component through the healthy knee kinematics and removing material from a tibial template. METHODS. LifeModeler KneeSIM software was used to analyze a biomimetic BCR implant (asymmetric tibia with convex lateral surface), a contemporary BCR (symmetric shallow dished tibia) and a contemporary CR (symmetric dished tibia) implant during simulated deep knee bend and chair sit. Components were mounted on an average bone model created from Magnetic Resonance Imaging (MRI) data of 40 normal knees. The soft-tissue insertions were obtained from the average knee model and the mechanical properties were obtained from literature. Femoral condyle center motions relative to the tibia were used to compare different implant designs. In vivo knee kinematics of healthy subjects from published literature was used for reference. RESULTS. During simulated deep knee bend, the ACL sacrificing contemporary CR implant showed initial posterior femoral subluxation due to the absent ACL, followed by paradoxical anterior sliding until 90° flexion, and no medial pivot rotation. Retention of the ACL in the contemporary BCR implant reduced the initial posterior shift of the femur in extension. However, medial pivot rotation and steady posterior rollback could not be achieved. In contrast, the biomimetic BCR implant showed knee motion very similar to that reported for healthy knees in vivo, with medial pivot rotation and greater, consistent rollback of the lateral femoral condyle than the medial condyle (11 mm medial vs. 16 mm lateral, Fig. 1 and Fig. 3). Similar trends were seen for all implants during simulated chair sit (Fig. 2 and Fig. 3). CONCLUSION. An ACL preserving biomimetic TKA implant was able to restore normal knee kinematics unlike contemporary ACL retaining and ACL sacrificing implants, during the simulated activities. This confirmed the hypothesis that a biomimetic articular surface together with ACL preservation is required to restore normal knee kinematics

Kinematics of the knee change during the full range of flexion [1]. The lateral femoral condyle (LFC) rolls back progressively through the entire range of flexion. The medial femoral condyle (MFC) does not move back during the first 110 degrees, but from 110 to 160 degrees it moves back by 10mm. This dual arc makes anatomical knee design a challenging task. In medial rotation, during flexion, the MFC stays in place, but the LFC moves forward in extension and backward in flexion. In lateral rotation the LFC stays still while the MFC moves back and forward in flexion and extension. During central rotation both condyles move reciprocally. However the knee is stable against an anteriorly or posteriorly directed force. It is important that all these degrees of freedom and stability are reproduced in total knee replacement (TKR) design. Furthermore, the two femoral condyles together form a spiral. Like the threads of a screw in a nut they allow medio-lateral translation of the femur [2] in the tibial reference frame. During flexion the knee centre moves laterally nearly 20% of the width of the tibial plateau and in extension the femur translates medially. This medio-lateral translation occurs in the natural normal knee joint. This has special significance in knee design because the natural femur (along with the trochlea) moves laterally in flexion, allowing the patella to be sited laterally, while most regular TKRs drive the patella medially. In order to test this anomaly we studied patellar maltracking in vivo and in cadavers. In vivo tracking studies using a patellar tracker during total knee replacement demonstrated average patellar maltracking of 10mm with regular TKR designs. Experiments on 22 cadaveric limbs using loaded quadriceps mechanism and trackers on the femur, tibia and patella, showed that in the natural knee the patella tracked medially by an average of 5mm. In regular TKRs the patella tracked medially. Compared to a normal knee, the patella in these designs maltracked on average by 10mm. Spiral condyles applied to the same bone cuts in the cadavers allowed the patella tracking to return to the expected lateral position in flexion. This has application to total knee replacement design. Unless the spiral design is incorporated in the condyles, patellar maltracking is inevitable and is likely to cause lateral knee pain and stiffness post-operatively

The natural knee allows multi-planar freedoms of rotation and translation, while retaining stability in the antero-posterior direction. It allows flexion with roll back, and medial, lateral and central rotation movements. The natural femoral condyles of the knee are spiral, therefore inducing a side to side translatory movement during flexion and extension. Incorporating all these features is vital in successful knee replacement design. The different knee designs currently in use demonstrate different deficiencies in knee function. A study of 150 Posterior Cruciate (PCL) Retaining Total Knee Replacements [1] has shown that in 72% of knees direct impingement of the tibial insert posteriorly against the back of the femur was responsible for blocking further flexion. The mean pre-operative range of flexion was 105° and post-operative was 105.9°. For every 2mm decrease in posterior condylar offset, the maximum flexion was reduced by 12.2°. The major disadvantage of the Posterior Stabilised (PS) Total Knee Replacement is gross anterior to posterior mid-flexion instability [2]. The Medial Rotation Total Knee Replacement is good in mid-flexion but not in high flexion where the femur slides forward on the tibia leading to impingement. The Birmingham Knee Replacement (BKR) is a rotating platform knee design which is stable throughout the range of flexion. In high flexion, the BKR brings the femur to the back of the tibia. The BKR also has spiral femoral condyles, matching the natural kinematics of the knee. The combined static and dynamic effect is 10mm lateral translation of the femur in flexion and vice versa in extension. Results for seventy nine BKRs (in seventy two patients) show the best Oxford Knee Score of 12 at follow up – excluding ten patients whose inferior scores were due to other pathologies. Knee flexion results show a 21° post-operative improvement in range of flexion. On objective independent testing, maximum walking speed is slower for patients with a standard knee replacement (6.5km/h) and the loading through the replaced side does not match the normal side. Comparatively, patients with a BKR have a faster maximum walking speed of 11km/h and the loading closely matches that of the normal knee. Studies based on the National Joint Register PROMs data [2] show that nearly thirty percent of Total Knee Replacement patients are not much better since their operation. A lot of improvement is needed in the design of knee replacements in order to achieve better function for knee replacement patients

High-energy injuries involving the proximal tibia sometimes result in significant soft tissue injuries that may create an incompetent knee extensor mechanism. Reconstruction of the extensor mechanism using the gastrocnemii has been previously described in those patients with tissue loss following either arthroplasty or tumour surgery. In 2009, a single cross-sectional study of eight patients described the technique after trauma, and their outcome at an average of 24 months. Use of a gastrocnemius rotational myoplasty has been described in the literature for six additional cases following trauma. We present our indications, technique and 5-year results of a separate series of four patients in whom the extensor mechanism of the knee was rendered incompetent after direct tissue loss, or subsequent infection, secondary to trauma. In each case, after stabilisation of the periarticular fracture and control of infection, the medial gastrocnemius was employed both to reconstruct the patellar ligament, and to simultaneously restore soft tissue coverage. Three out of 4 patients had excellent outcomes, have returned to their previous occupations and participate in regular sport. The overall mean scores were: Oxford knee Score (38.25), Knee Injury and Osteoarthritis Outcome Score (KOOS) (64.5) and Modified Cincinnati Score (68.25). Mean knee ROM was 5–97 degrees. Video for basic gait analysis was recorded. For those traumatic injuries with the difficult combination of a soft tissue deficit and incompetence of the knee extensor mechanism, we believe the medial gastrocnemius rotational myoplasty provides an excellent reconstructive option to address both of these fundamental problems simultaneously

Introduction:. Contemporary Posterior Cruciate Ligament (PCL) retaining TKA implants (CR) are associated with well-known kinematic deficits, such as absence of medial pivot motion, paradoxical anterior femoral sliding, and posterior femoral subluxation at full extension. The hypothesis of this study was that a biomimetic implant, reverse engineered by using healthy knee kinematics to carve the tibial articular surface, could restore normal kinematic patterns of the knee. Methods:. Kinematics of the biomimetic CR and two contemporary CR implants (A, B) were evaluated during simulated deep knee bend and chair-sit in LifeModeler KneeSIM™ software. Anteroposterior motion of the medial and lateral femoral condyle centers was measured relative to a tibial origin. The implants were mounted on an average knee model created from magnetic resonance imaging (MRI) of 40 healthy knees. The medial and lateral collateral ligaments, posterior cruciate ligament, quadriceps mechanism, and the overall capsular tension were modeled. The soft-tissue insertions were obtained from the average knee model, and the mechanical properties were obtained from literature. In vivo knee kinematics of healthy subjects from published literature was used for reference. Results:. During the simulated deep knee bend, the biomimetic CR showed knee motion similar to that reported for healthy knees in vivo, with an overall medial pivot and greater rollback of the lateral femoral condyle than the medial condyle (7.2 mm medial vs. 13.2 mm lateral, Fig 1. and Fig. 3). In contrast, contemporary CR-A showed no medial pivot rotation, and the femur underwent paradoxical anterior sliding from 0 deg to 90 deg flexion. Contemporary CR-B did not show paradoxical anterior femoral sliding. However, contemporary CR-B also did not show medial pivot and the posterior rollback of the medial femoral condyle was slightly greater than that of the lateral condyle (9.7 mm medial vs. 7 mm lateral). Similar trends were seen for all implants during the simulated chair sit (Fig 2. and Fig. 3). Conclusion:. The results confirmed the hypothesis that, during the simulated activities, the biomimetic CR implant could provide kinematics similar to that reported for healthy knees, unlike contemporary CR implants. The biomimetic implant showed medial pivot motion with greater rollback of the lateral femoral condyle than the medial condyle. In contrast, the contemporary implants showed several abnormalities including absence of medial pivot, paradoxical anterior femoral sliding and reduced posterior rollback