Introduction

Body mass index (BMI) is a topical area of interest in the field of lower limb arthroplasty. It has been well established that BMI can influence post-operative outcomes. This study compares post-operative outcomes, including satisfaction rates, length of stay (LOS) and radiographic findings in different BMI groups following total hip arthroplasty (THA).

Background

The literature quotes up to 20% dissatisfaction rates for total knee replacements (TKR). Swedish registry and national joint registry of England and Wales confirm this with high volumes of patients included. This dissatisfaction rate is used as a basis for improving/changing/modernising knee implant designs by major companies across the world.

The restoration of knee alignment is an important goal during total knee arthroplasty (TKA). In the past surgeons aimed to restore neutral limb alignment during surgery. However, previous studies have demonstrated alignment to be dynamic, varying depending on the position of the limb and the degree of weight-bearing, and between patients. We used a validated computer navigation system to measure the femorotibial mechanical angle (FTMA) in 264 knees in 77 male and 55 female healthy volunteers aged 18 to 35 years (mean 26.2). We found the mean supine alignment to be a varus angle of 1.2° (standard deviation (sd) 4), with few patients having neutral alignment. FTMA differs significantly between males and females (with a mean varus of 1.7° (sd 4) and 0.4° (sd 3.9), respectively; p = 0.008). It changes significantly with posture, the knee hyperextending by a mean of 5.6°, and coronal plane alignment becoming more varus by 2.2° (sd 3.6) on standing compared with supine.

Knee alignment is different in different individuals and is dynamic in nature, changing with different postures. This may have implications for the assessment of alignment in TKA, which is achieved in non-weight-bearing conditions and which may not represent the situation observed during weight-bearing.

Cite this article: Bone Joint J 2015; 97-B:498–502

Objectives

Acetabular component orientation in total hip arthroplasty (THA) influences results. Intra-operatively, the natural arthritic acetabulum is often used as a reference to position the acetabular component. Detailed information regarding its orientation is therefore essential. The aim of this study was to identify the acetabular inclination and anteversion in arthritic hips.

Introduction:

Restoration of normal hip biomechanics is vital for success of total hip arthroplasty (THA). This requires accurate placement of implants and restoration of limb length and offset. The purpose of this study was to assess the accuracy of computer navigation system in predicting cup placement and restoring limb length and offset.

The problem associated with ceramic on ceramic total hip replacement (THR) is audible noise. Squeaking is the most frequently documented sound. The incidence of squeaking has been reported to wide range from 0.7 to 20.9%. Nevertheless there is no study to investigate on incidence of noise in computer assisted THR with ceramic on ceramic bearing. The purpose of this study was to determine the incidence and risks factors associated with noise. We retrospectively reviewed 200 patients (202 hips) whom performed computer assisted THR (Orthopilot, B. Braun, Tuttlingen, Germany) with ceramic on ceramic bearing between March 2009 and August 2012. All procedures underwent uncemented THR with posterior approach by single surgeon. All hips implanted with PLASMACUP and EXIA femoral stem (B. Braun, Tuttlingen, Germany). All cases used BIOLOX DELTA (Ceramtec, AG, Plochingen, Germany) ceramic liner and head. The incidence and type of noise were interviewed by telephone using set of questionnaire. Patient's age, weight, height, body mass index, acetabular cup size, femoral offset size determined from medical record for comparing between silent hips and noisy hips. The acetabular inclination angle, acetabular anteversion angle, femoral offset, hip offset were reviewed to compare difference between silent hips and noisy hips. The audible noise was reported for 13 hips (6.44%). 5 patients (5 hips) reported click (2.47%) and 8 patients (8 hips) squeaked (3.97%). The mean time to first occurrence of click was 13.4 months and squeak was 7.4 months after surgery. Most common frequency of click was less than weekly (60%) and squeak was 1–4 times per week (50%). Most common activity associated with noise was bending; 40% in click and 75% in squeaking. No patients complained for pain or social problem. Moreover, no patient underwent any intervention for the noise. The noise had not self-resolved in any of the patients at last follow up. Age, weight, height and BMI showed no statistically significant difference between silent hips and click hips. In addition, there was also same result between silent hips and squeaking hips. Acetabular cup insert size and femoral offset stem size the results showed that there was no statistically significant difference between silent hips and click hips, also with squeaking hips. Acetabular inclination, angle acetabular anteversion angle, femoral offset, hip offset the results shown that only acetabular anteversion angle differed significantly between silent hips (19.94±7.78 degree) and squeaking hips (13.46±5.54 degree).

The results can conclude that incidence of noise after ceramic on ceramic THR with navigation was 6.44 %. Squeaking incidence was 3.97% and click incidence was 2.47%. The only associated squeaking risk factor was cup anteversion angle. In this study, squeaking hip had cup anteversion angle significant less than silent hip.

Introduction:

The transverse acetabular ligament (TAL) antomy is not a well explored aspect of the hip joint with limited morphological description in the reviewed literature. It is often used as an anatomical landmark for orientation of the acetabular component in total hip arthroplasty (THA). There is debate as to whether it represents an appropriate guide to cup placement in THA. Present descriptions in orthopaedic literature conside it as a single plane structure to which the surgeon can align the cup. The aim of the current study was to investigate the morphology of the TAL and it was hypothesised that the current description of it being a plane would prove insufficient.

Introduction

Malalignment of lower limb is a common feature in patients with osteoarthritis (OA). This, either cause or effect of OA, is known to alter the normal anatomy of knee and affects progression of wear and tear in mechanically stressed compartment. We investigated the relationship of mechanical axis to wear and tear in varus, neutral and valgus knees.

In arthritic knees with severe valgus deformity Total Knee Arthroplasty (TKA) can be performed through medial or lateral parapatellar approaches. Many orthopaedic surgeons are apprehensive of using the lateral parapatellar approach due to lack of familiarity and concerns about complications related to soft tissue coverage and vascularity of the patella and the overlying skin. However surgeons who use this approach report good outcomes and no added complications. The purpose of our study was to compare outcomes following TKA performed through a medial parapatellar approach with those performed through a lateral parapatellar approach in arthritic knees with severe valgus deformity.

We conducted a retrospective review of patients from two consultants using computer navigation for all their TKAs. All patients with severe valgus deformities (Ranawat 2 & 3 grades) operated on between January 2005 and December 2011 were included. 66 patients with 67 TKAs fulfilled the inclusion criteria. Patients were group by approach; Medial = 34TKAs (34 patients) or Lateral = 33 TKAs (32 patients). Details were collected from patients' records, AP hip-knee-ankle (HKA) radiographs and computer navigation files. Outcome measures included lateral release rates, post-operative range of knee movements, long leg mechanical alignment measurements, post-operative Oxford scores at six weeks and one year, patient satisfaction and any complications. Comparisons were made between groups using t-tests.

The total cohort had a mean age of 69 years [42–82] and mean BMI of 29 [19–46]. The two groups had comparable pre-operative Oxford scores (Medial 41[27–56], Lateral 44 [31–60]) and pre-operative valgus deformity measured on HKA radiographs (Medial 13° [10°–27.6°], Lateral 12° [6°–22°]). Three patients in the Medial group underwent intra-operative lateral patellar release to improve patellar tracking. Seven patients in the Lateral group had a lateral condyle osteotomy for soft tissue balancing (one bilateral). There was no statistically significant difference between groups at one year follow up for maximum flexion (Medial 100° [78°–122°], Lateral 100° [85°–125°], p=0.42), fixed flexion deformity (Medial 1.2° [0°–10°], Lateral 0.9° [0°–10°], p=0.31) or Oxford score (Medial 23 [12–37], Lateral 23 [16–41], p=0.49). Similarly there was no difference in the patient satisfaction rates between the two groups at one year follow up. However there was a statistically significant difference in the mean radiographic post-operative alignment angle measurement (Medial 1.8° valgus [4° varus to 10° valgus], Lateral 0.3° valgus [5° varus to 7° valgus], p=0.02). One patient in the Medial group had a revision to hinged knee prosthesis for post-operative instability. There was no wound breakdown or patellar avascular necrosis noted in either of the groups.

The lateral parapatellar approach resulted in slightly better valgus correction on radiographs taken six weeks post-operatively. We found no major complications in the Lateral parapatellar approach group. Specifically we did not encounter any difficulties in closing the deep soft tissue envelope around the knee and there were no cases of patellar avascular necrosis or skin necrosis. Hence we conclude that lateral parapatellar approach is a safe and reliable alternative to the medial parapatellar approach for correction of severe valgus deformity in TKA.

This study measured the three bony axes usually used for femoral component rotation in total knee arthroplasty and compared the accuracy and repeatability of different measurement techniques.

Fresh cadaveric limbs (n=6) were used. Three observers (student, trainee and consultant) identified the posterior condylar (PCA), anteroposterior (AP) and the transepicondylar (TEA) axes, using a computer navigation system to record measurements. The AP axis was measured before and after being identified with an ink line. The TEA was measured by palpation of the epicondyles both before and after an incision was made in the medial and lateral gutters at the level of the epicondyles, allowing the index finger to be passed behind the gutters. In addition the true TEA was identified after dissection of all the soft tissues. Each measurement was repeated three times. For all axes and each observer the repeatability coefficient was calculated.

The identification of the PCA was the most reliable (repeatability coefficient: 1.1°) followed by the AP after drawing the ink line (4.5°) then the AP before (5.7°) and lastly the TEA (12.3°) which showed no improvement with the incisions (13.0°). In general the inter-observer variability for each axis was small (average 3.3°, range 0.4° to 6°), being best for the consultant and worst for the student. In comparison to the true TEA, the recorded TEA and AP axis averaged within 1.5° whilst the PCA was consistently 2.8° or more internally rotated.

This study echoed previous studies in demonstrating that palpating the PCA intra-operatively is highly precise but was prone to errors in representing the true TEA if there was asymmetrical condylar erosion. The TEA was highly variable irrespective of observer ability and experience. The line perpendicular line to the AP axis most closely paralleled the true TEA when measured after being identified with an ink line.

INTRODUCTION

Leg length discrepancy following total hip arthroplasty (THA) can be functionally disabling for affected patients and can lead on to litigation issues. Assessment of limb length discrepancy during THA using traditional methods has been shown to produce inconsistent results. The aim of our study was to compare the accuracy of navigated vs. non navigated techniques in limb length restoration in THA.

Introduction

Restoration of normal hip biomechanics is vital for success of total hip arthroplasty (THA). This requires accurate placement of implants and restoration of limb length and offset. The purpose of this study was to assess the precision and accuracy of computer navigation system in predicting cup placement and restoring limb length and offset.

Introduction

Malalignment of cup in total hip replacement (THR) increases rates of dislocation, impingement, acetabular migration, pelvic osteolysis, leg length discrepancy and polyethylene wear. Many surgeons orientate the cup in the same anteversion and inclination as the inherent anatomy of the acetabulum. The transverse acetabular ligament (TAL) and acetabular rim can be used as a reference. No study has yet defined the exact orientation of the TAL. The aim of this study was to describe the orientation of acetabular margin and compare it with TAL orientation.

Introduction

Success of total hip replacement (THR) is closely linked to positioning of the acetabular component. Malalignment increases complication rates. Our aim was to describe the anteversion and inclination of the inherent acetabulum in arthritic hips and identify the number that fall out with the ‘safe zone’ of acetabular position described by Lewinnek et al. (anteversion 15±10 degrees; inclination 40±10 degrees).

Introduction

Soft tissue balancing is an important aspect of total knee replacement surgery. Traditionally sequential medial soft tissue release is performed for balancing in varus deformity. Its effects on kinematics and dynamic Femoro-Tibial-Mechanical-Angle (FTMA) have been described in extension and 90° flexion in coronal plane. However most studies have missed what happens when the knee flexes from 0 to 90 degrees This study is one of the first to describe its effects on knee kinematics throughout flexion. The aim was to look at deviation of FTMA in coronal plane with traditional sequential medial release with and without measured stress applied in varus and valgus at each point of measurement through the range of flexion.

Introduction

The success of total hip replacement (THR) is closely linked to the positioning of the acetabular component. Malalignment increases rates of dislocation, impingement, acetabular migration, pelvic osteolysis, leg length discrepancy and polyethylene wear. Many surgeons orientate the cup to inherent anatomy of the acetabulum. Detailed understanding of the anatomy and orientation of the acetabulum in arthritic hips is therefore very important. The aim of this study was to describe the anteversion and inclination of the inherent acetabulum in arthritic hips and to identify the number that fall out with the ‘safe zone’ of acetabular position described by Lewinnek et al. (anteversion 15°±10°; inclination 40°±10°).

Traditionally sequential medial soft tissue release is performed for balancing in total knee arthroplasty for varus knees. Its effects on kinematics have been described in extension and 90° flexion in coronal plane. This is the first study to describe its effects on kinematics throughout flexion. 12 cadaveric knees were studied using a computer navigation system to assess kinematics. Femoro-Tibial-Mechanical-Angle(FTMA) was studied in extension, 0°, 5°, 30°,45°,60°,90° and maximum flexion. Sequential medial release was performed in 7 steps, described by Luring et al(Ref). At each step FTMA was measured without and with stressing. A 10 Newton Meter moment arm was applied for varus and valgus stress. Most of the initial release steps had little effect on FTMA without force applied, especially in the initial 60° of flexion. Application of varus force demonstrated very small changes. Application of valgus force demonstrated little change in initial arc of flexion until step 5 was reached (Table 1). Our study concludes the present sequence of medial release may not be correct and should be further investigated to modify the sequence for soft tissue balancing in TKR surgery.

The aim of the study was to investigate rotational behaviour of the arthritic knee before (preimplant) and after (postimplant) total knee replacement (TKR) using (image-free navigation system as a measurement tool which recorded the axial plane alignment between femur and tibia, in addition to the coronal and sagittal alignment as the knee is flexed through the range of motion. The data on the rotation of the arthritic knee was collected after the knee exposure and registration of the lower limb (preimplant data). The position of rotation between the femur and tibia was recorded in 30° flexion, 45°, 60°, 90° and maximum degrees of flexion of the knee. The data was divided into subsets of varus and valgus knees and these were analysed pre and postimplant for their rotational position using SPSS for statistics.

The system was used in 117 knees of which 91 had full data set available (43 male 48 female). These included 71 varus knees, 16 valgus knees and 4 neutral knees to start in extension. Preimplant data analysis revealed there is tendency for the arthritic knees to first go in internal rotation in the initial part of flexion to 30 degrees and then the rotation is reversed back. This happens irrespective of the initial starting rotational relationship between femur and tibia in full extension. This happens in both varus as well as valgus arthritic knees. This trend of internal rotation in this initial part of flexion is followed in TKR as well implanted with fixed bearing CR knees irrespective of the preoperative deformity. Also noteworthy was the difference in rotation at 30°, 60° and 90 degrees of flexion between preimplant and postimplant knees (irrespective of varus and valgus groups).

When calculated at different points of flexion, there was statistically significant difference in the change of rotation at each point of flexion except 45 degree of flexion. The pre-operative values of change in rotation (internal being positive) at each step from the extended position being 5.4° (SD 4.5°) at 30 ° flexion, 4.7°(5.2°) at 45°, 3.6°(6.1°) at 60°, 3.5°(7.2°) at 90° and 4.2°(8.3°) at maximum flexion. Corresponding post-operative rotations were 2.2°(4.8°), 4.1°(6.4°), 6.6°(7.3°), 9.9°(8.8°) and 7.7°(8.9°). There was also an increase in the total range of rotation that the knee goes through after it has been implanted with prosthesis although it may not happen in every knee. This is statistically significant (p value <0.001) and seems more so in valgus group. The rotational movements and interrelationship of the femur and tibia is a complex issue, especially in the arthritic knees. Preimplant arthritic knee behaved generally similarly to normal knees according to the literature. Normal gait pattern demonstrates that the tibia moved through a 4° to 8° arc of internal rotation relative to the femur. The overall range (10.2° =/−4.2°) of knee rotation in this study greater than 8° might be explained by preimplant data acquired after the knee was approached and therefore releasing knee soft tissue envelop. This study confirmed that during the first 30° both varus and valgus knees moved internally. In our study there is increased range of total rotation postimplant (14° =/−6.8°) which may be explained by the fact that the anterior cruciate ligament is lost in all the TKRs and the posterior cruciate ligament may be dysfunctional as well. Thus the constraints on the knee rotation are decreased postimplant leading to increased rotation. We found some difference between varus and valgus post implant knees in that internal rotation seen in initial 30 degrees of flexion is much more pronounced in valgus knees as compared to varus knees (p value <0.001). This study confirmed knee internal rotation in initial stages of flexion, preimplant in arthritic knees during a passive knee flexion assessment. Varus and valgus knee seemed to behave similarly. This mimics the normal knee rotation. Postimplant knees in TKR behave differently.

The success of total hip replacement (THR) is closely linked to the positioning of the acetabular component. Malalignment increases rates of dislocation, impingement, acetabular migration, pelvic osteolysis, leg length discrepancy and polyethylene wear. Many surgeons orientate the cup in the same anteversion and inclination as the inherent anatomy of the acetabulum. The transverse acetabular ligament and acetabular rim can be used as a reference points for orientating the cup this way. Low rates of dislocation have been reported using this technique. Detailed understanding of the anatomy and orientation of the acetabulum in arthritic hips is therefore very important. The aim of this study was to describe the anteversion and inclination of the inherent acetabulum in arthritic hips and to identify the number that fall out with the ‘safe zone’ of acetabular position described by Lewinnek et al. (anteversion 15°±10°; inclination 40°±10°).

A series of 65 hips, all with symptomatic osteoarthritis undergoing THR were investigated. Patients with developmental dysplastia of hip (DDH) were excluded. All patients had a navigated THR as part of their normal clinical treatment. A posterior approach to the hip was used. A commercially available non image based computer navigation system (Orthopilot BBraun Aesculap, Tuttlingen, Germany) was used. Rigid bodies (using active trackers) were attached to pelvis and femur. Anterior pelvic plane was registered using the two anterior superior iliac spines and pubic symphysis. The femoral head dislocated and removed and the labrum and soft tissue were excised to clear floor and rim of the acetabulum. Inner size of the empty acetabulum was sized with cup trials and appropriately size trial fixed with a computer tracker was then aligned in the orientation of the natural acetabulum as defined by the acetabular rim ignoring any osteophytes. The inclination and anteversion were calculated by the software. Surgery then proceeded with guidance of the computer navigation system. The computer software defines the anatomical values of orientation, to allow comparison with radiographs these were converted to radiological values as described by Murray et al. The acetabular inclination in all hips was also measured on pre-operative anteroposterior pelvic radiographs. This was done using digital radiographs analysed with the PACS system (Kodak, Carestream PACS Client, version 10.0). Acetabular inclination was measured using as the angle between a line passing through the superior and inferior rim of the acetabulum and a line parallel to the pelvis as identified by the tear drops, using the method described by Atkinson et al.

All patients were Caucasian and had primary osteoarthritis. There were 29 males and 36 females. The average age was 68 years (SD 8). Mean anteversion was 9.3° (SD 10.3°). Anteversion for males was significantly lower than females with a mean difference of −5.5° (95%CI −10.5°,−0.5°) p = 0.033 but there was no significant difference in the number falling outside the “safe zone”. Mean inclination was 50.4° (SD 7.4°). There was no significant difference between males and females with respect to inclination angle or the number that fell outside the “safe zone”. Overall 69% of patients had a combined inclination and anteversion of the native acetabulum that fell outside the “safe zone” of Lewinnek.

Mean acetabular inclination falls out with the ‘safe zone’. This trend has been seen in a recent study of arthritic hips using CT scans which found that the average angle of inclination in both males and females was greater than the upper limit of the safe zone. This study using CT also demonstrated a statistically significant 5.5° difference between males and females in terms of anteversion. This is the same as the figure we have found in our work. Inherent acetabular orientation in arthritic hips falls out with the safe zone defined by Lewinnek in 69% of cases. When using the natural acetabular orientation as a guide for positioning implants it should therefore not be assumed this will fall with in the safe zone although the validity of safe zones itself is questionable. Variation between patients must be taken into account and the difference between males and females, particularly in terms of anteversion, should also be considered.

We compared lower limb coronal alignment measurements obtained pre- and post-operatively with long-leg radiographs and computer navigation in patients undergoing primary total knee replacement (TKR). A series of 185 patients had their pre- and post-implant radiological and computer-navigation system measurements of coronal alignment compared using the Bland-Altman method. The study included 81 men and 104 women with a mean age of 68.5 years (32 to 87) and a mean body mass index of 31.7 kg/m² (19 to 49). Pre-implant Bland–Altman limits of agreement were -9.4° to 8.6° with a repeatability coefficient of 9.0°. The Bland–Altman plot showed a tendency for the radiological measurement to indicate a higher level of pre-operative deformity than the corresponding navigation measurement. Post-implant limits of agreement were -5.0° to 5.4° with a repeatability coefficient of 5.2°. The tendency for valgus knees to have greater deformity on the radiograph was still seen, but was weaker for varus knees.

The alignment seen or measured intra-operatively during TKR is not necessarily the same as the deformity seen on a standing long-leg radiograph either pre- or post-operatively. Further investigation into the effect of weight-bearing and surgical exposure of the joint on the mechanical femorotibial angle is required to enable the most appropriate intra-operative alignment to be selected.