Less valgus alignment in total knee arthroplasty for the varus knee

Constitutional varus of the leg is well recognizable anatomically. Moreland[1] studied long standing radiographs of normal males with a range of varus from 2.6-3° in the proximal tibia. Victor et al. [2] reported constitution varus of 3 degree in 32% men, 17% women. The authors routine technique during total knee arthroplasty (TKA) is to cut the distal femur at 5° valgus and the tibia at neutral for the valgus leg and cut the distal femur at 5° valgus and the tibia 2° varus for varus aligned limbs. 127 consecutive long standing knee radiographs were not retrospectively studied pre and post operatively with 2 year minimum follow up. Average age was 68 years (range 51-90). Average weight was 215 lbs (range 110 – 333). Average tourniquet time was 32 minutes for all patients prior to closure.For the varus group (72 knees), average pre-op tibial femoral alignment was 3.3° varus (range 0-13°). Post-op tibial femoral alignment was 1.2° valgus (range 1° varus - 5° valgus) with the mechanical axis falling into the medial compartment in all patients. Average pre-op knee score was 88 and post-op was 180 at minimum of 2 years.For the valgus group (55 knees), average pre-op tibial femoral alignment was 7.5° (range 2°-24°) valgus. Average post-op tibial femoral alignment was 3.8° (range 1°-10°) valgus. Average pre-op knee score was 107 and post-op was 182 at minimum of 2 years. The authors agree with aiming for valgus alignment for the classic valgus leg (mechanical axis centered on hip, knee, ankle) and less valgus alignment for the varus knee (mechanical axis into the medial compartment). Following the patients anatomy eliminates the need for major soft tissue releases while still avoiding “malalignment”. No special soft tissue releases were required in any patient with pre-op varus or valgus alignment. The clinical outcome is not effected by leaving pre-op varus aligned extremities in less valgus with their TKA’s.     

Varus Gonarthrosis Predisposes to Varus Malalignment in TKA

Postoperative alignment is a predictor for long-term survival of total knee arthroplasty (TKA). The purpose of this study was to evaluate whether or not preoperative deformities predispose to intraoperative malposition of TKA components. A retrospective radiographic analysis of 53 primary TKA cases was performed. Preoperative AP hip to ankle and lateral knee radiographs were compared with postoperative views to evaluate component positioning. The following angles were measured: the hip–knee–ankle (HKA) angle expressing the mechanical axis of the leg, the mechanical lateral distal femur angle (mLDFA), the medial proximal tibia angle (MPTA), the posterior distal femur angle (PDFA), and the posterior proximal tibia angle (PPTA). Postoperative measurement of the HKA revealed 34.0% of the cases had a deviation of >±3° from neutral alignment. Sixteen knees (30.2%) were in varus and, with one exception, all presented with severe varus gonarthrosis prior to surgery with a mean tibiofemoral angle of 12.4° compared with 1.0° of valgus in the optimally aligned group. Patients (93.3%) with preoperative valgus malalignment showed optimal postoperative HKA. Odds ratios for malalignment of TKA for varus knees in comparison with valgus knees were 7.1 for HKA, 2.4 for MPTA, 4.9 for PDFA, and 1.7 for PPTA. The overall number of outliers in the presented data corresponds well with reports from other authors using different implants and guide systems. The presented data indicate that patients with preoperative varus alignment have a higher risk of postoperative implant malposition than patients with valgus alignment. The data supports that preoperative varus deformity predisposes to varus malposition of TKA. The risk for intraoperative malposition is significantly lower in valgus knees.     

Catastrophic Varus Collapse of the Tibia in Obese Total Knee Arthroplasty

Background

Mechanical complications have been underemphasized in reports on total knee arthroplasty (TKA) in obese patients. Noticing an increased prevalence of varus collapse of the tibia in obese total knee patients, we sought to determine if variability in proximal tibial cancellous bone strength played a role in failure. We attempted to define a cancellous threshold above which alternative methods of fixation should be used.

Lower limb alignment in healthy Japanese adults

BackgroundKnowledge regarding the normal alignment of the lower limb is important when considering alignment for total knee arthroplasty. However, few studies have explored the lower limb alignment of healthy Japanese subjects.MethodsBetween July and October 2020, we performed whole leg standing radiography of 120 legs of 60 healthy adult Japanese volunteers aged <50 years in the closed-leg stance. The measurement parameters were hip knee ankle angle (positive for varus), percentage of constitutional varus (hip knee ankle angle ≥ 3°), mechanical axis deviation ratio, mechanical lateral distal femoral angle, medial proximal tibial angle, joint line convergence angle (positive for lateral opening), and tibial joint line angle (positive for medial inclination).ResultsThe mean measured values for all volunteers, men and women, were as follows: hip knee ankle angle (°), 2.3, 2.6, and 2.0; mechanical axis deviation ratio, 35.8, 35.6, and 36.9; mechanical lateral distal femoral angle (°), 86.7, 87.0, and 86.7; medial proximal tibial angle (°), 85.6, 85.0, and 86.2; joint line convergence angle (°), 0.6, 0.3, and 0.8; and tibial joint line angle (°), ?1.0, ?0.7, ?1.4, respectively. The percentage of constitutional varus was 35.8% overall, 35.8% in men and 35.3% in women. Only the medial proximal tibial angle was smaller in men than that in women (p = 0.003).ConclusionsThe mechanical lateral distal femoral and medial proximal tibial angles were smaller, hip knee ankle angle was larger, and percentage of constitutional varus was higher in Japanese subjects than those reported for subjects in other countries. Our findings improve the understanding of Japanese-specific alignments when considering alignment for lower limb surgery, especially, total knee arthroplasty.     

Endosteal referencing in revision total knee arthroplasty

A method of orienting the femoral and tibial bone cuts relative to the endosteal cortex of the femur and tibia was used in 32 patients who underwent revision total knee arthroplasty. The mean orientation of the femoral component was 96.74° ± 1.03°, mean orientation of the tibial baseplate was 90.71° ± 1.10°, mean anatomic tibiofemoral alignment was 7.42° ± 1.69° of valgus, and mean mechanical tibiofemoral alignment was 1.09° ± 1.83° of valgus. Mean tibial bowing was 1.63° ± 1.57° of valgus, and mean femoral bowing was 0.58° ± 1.53° of varus. Valgus tibial bowing was correlated with valgus orientation of the tibial component (r = .86, P < .000001), and varus femoral bowing was correlated with orientation of the femoral component (r = .54, P = .0054). Referencing the implant position from the endosteal cortex of the intramedullary canals provides a reliable method of achieving satisfactory alignment in most revision total knee arthroplasties; however, bowing of the femur or tibia can affect alignment.     

Unicompartmental knee arthroplasty in middle-aged patients: A 2- to 6-year follow-up evaluation

Twenty-eight unicompartmental knee arthroplasties performed as an alternative to high tibial osteotomy or tricompartmental knee arthroplasty in patients under 60 years of age were reviewed after 2 to 6 years of follow-up. The patient's age at the time of operation averaged 52 years. Using the Knee Society Score, 90% were rated good or excellent results in terms of function and pain relief. The average flexion angle obtained was 124°, and the average postoperative alignment was 4° of anatomic valgus for varus deformities and 8° for valgus deformities. The average activity level according to the Tegner and Lysholm score slightly improved (preoperative, 2.3; follow-up, 2.7 points). Of the 28 knees, 9 (32%) presented radiolucent lines about the tibial component and two had incomplete radiolucent lines at the bone-cement interface on the femoral side. There was no correlation between activity level and tibial radiolucent lines. Two revisions were performed because of loosening of the femoral component at the prosthesis-cement interface. One was converted to another unicompartmental arthroplasty and the other to a tricompartmental arthroplasty. One tibial component exhibited an asymptomatic slowly progressive radiolucency. Unicompartmental knee arthroplasty in middle-aged patients yields 2- to 6-year results competitive with osteotomy but inferior to tricompartmental arthroplasty in terms of revision. The specific prosthetic design used in this series appeared to be vulnerable to femoral component loosening possibly because of constrained tibial topography and smooth tapered femoral fixation lugs.     

Autogenous bone grafting for severe angular deformity in total knee arthroplasty

Fourteen patients with severe angular knee deformities (range, 30 degrees varus to 35 degrees valgus) had total knee arthroplasty using autogenous bone graft to the tibia. Twelve knees had osteoarthritis, one rheumatoid arthritis, and one gouty arthritis. The preoperative knee motion averaged -5 degrees of extension to 80 degrees of flexion and the average motion arc was 70 degrees. All tibial defects were greater than 25% of the tibial component support surface and more than 10 mm deep. Twelve knees were reconstructed with Insall-Burstein posterior stabilized total condylar knee implants and two knees, with severe preoperative ligamentous instability, with the constrained Total Condylar III implant. Postoperative rehabilitation was routine, and weight bearing was begun, on average, on the third postoperative day. The follow-up period averaged 4.1 years (range, 2-7.3 years). Radiographic analysis revealed no change in knee or component alignment compared with immediate postoperative position. All grafts consolidated without evidence of collapse, resorption, or prosthetic subsidence. All patients had good or excellent clinical results (Hospital for Special Surgery Knee Rating Scale). The average postoperative arc of motion was 90 degrees. There were no infections and no need for implant removal. The technique developed by the senior author (T.P.S.) utilizes bone resected from the distal femur during knee arthroplasty. An oblique planar cancellous surface is created on the recipient side, and coaptation of cancellous distal femoral graft surface to this recipient bed is ensured by vitallium screw fixation. The proximal tibia is reconstituted by the graft, and subchondral femoral bone after shaping of the graft forms the tibial periphery.     

Radiographic Findings in Patients With Catastrophic Varus Collapse After Total Knee Arthroplasty

Background

Catastrophic varus collapse is an uncommon mechanism of failure in primary total knee arthroplasty (TKA). Varus collapse has been associated with obesity and smaller implant sizes. However, to our knowledge, preoperative radiographic characterization of this cohort has not been performed. Therefore, the following study evaluated preoperative alignment and how this correlates with the degree of eventual varus collapse identified in this patient population prior to revision.

Intramedullary control of distal femoral resection results in precise coronal alignment in TKA

Introduction

There is still a relevant rate of outliers in coronal alignment >3° when the conventional technique is used, potentially accompanied by a poorer long-term clinical outcome and a reduced longevity of the implant. Intraoperative implementation of preoperative planning and above all checking of the bone resections carried out are decisive for reinstating a straight leg axis. Intramedullary control of femoral resection has not been described to date. The objective of this study was to present a new technique for the intramedullary control of femoral resection and the results obtained using this method.

Methods

All patients who underwent primary total knee arthroplasty with the new intramedullary control of femoral resection were included in this retrospective study. The frequency of the need for correction of the saw cuts was documented. The radiological assessment included pre- and postoperative whole-leg standing radiographs. In the process, the whole-leg axis, AMA, entry point, LDFA and MPTA were evaluated preoperatively. On the postoperative radiographs, the whole-leg axis and the alignment of the femoral and tibial components were evaluated.

Results

One hundred and sixty-two total knee arthroplasties (TKAs) were included in the study. The average age was 68.7 years. The preoperative malalignment was on the average 8.2° ± 4.7° (23.8° varus to 17.3° valgus). The postoperative whole-leg axis was on the average 1.3° ± 1.1° (5.5° varus to 4.3° valgus). The femoral component showed a deviation from the mechanical axis of 0.1° ± 1.2° (4.3° varus to 3.7° valgus) and the tibial component a deviation from the mechanical tibial axis of 0.3° ± 1.2° (4.2° varus to 2.5° valgus).

Conclusions

The new technique of intramedullary control of distal femoral resection, together with preoperative planning, leads to a precise alignment of the femoral component in the coronal plane. Thus, for the first time, a simple and effective tool for checking distal femoral resection is available for standardized use.     

The Impact of Coronal Alignment on Revision in Medial Fixed-Bearing Unicompartmental Knee Arthroplasty

BackgroundTo better define the optimal alignment target for medial fixed-bearing unicompartmental knee arthroplasty (UKA), this study compares the postoperative mechanical alignment of well-functioning UKAs against 2 groups of failed UKAs, including revisions for progression of lateral compartment osteoarthritis (“Progression”) and revisions for aseptic loosening or subsidence (“Loosening”).MethodsFrom our prospective institutional database of 3351 medial fixed-bearing UKAs performed since 2000, we identified 37 UKAs revised for Progression and 61 UKAs revised for Loosening. Each of these revision cohorts was matched based on age at surgery, gender, body mass index, and postoperative range of motion with unrevised UKAs that had at least 10 years of follow-up and a Knee Society Score of 70 or greater without subtracting points for alignment (“Success” groups). Postoperative alignment was quantified by the hip-knee-ankle (HKA) angle measured on long-leg alignment radiographs.ResultsThe mean HKA angle at 4-month follow-up for the Progression group was 0.3° ± 3.6° of valgus compared to 4.4° ± 2.6° of varus for the matched Success group (P < 0.001). For the Loosening group, the mean HKA angle was 6.1° ± 3.1° of varus versus 4.0° ± 2.7° of varus for the matched Success group (P < 0.001).ConclusionsPatients with well-functioning UKAs at 10 years exhibited mild varus mechanical alignment of approximately 4°, whereas patients revised for progression of osteoarthritis averaged more valgus and those revised for loosening or subsidence averaged more varus. The optimal mechanical alignment for medial fixed-bearing UKA survival with contemporary polyethylene is likely slight varus.     

Relationship Between Coronal Alignment and Rotational Profile of Lower Extremity in Patients With Knee Osteoarthritis

Background

We aimed at determining whether the coronal alignment of lower extremity was related to rotational geometry of distal femur, femoral anteversion, and tibial torsion in patients with knee osteoarthritis.

Total knee arthroplasty after varus osteotomy of the distal part of the femur

BACKGROUND: There is little information in the literature regarding the outcome of total knee arthroplasty following distal femoral varus osteotomy. The purpose of the present study was to evaluate the intermediate-term results of total knee arthroplasty following distal femoral varus osteotomy. METHODS: The study group consisted of nine consecutive patients (eleven knees) who had had a total knee arthroplasty following varus osteotomy of the distal part of the femur. The average age of the patients was forty-four years (range, fifteen to seventy years) at the time of the arthroplasty. The results were evaluated with use of the Knee Society score preoperatively and after a mean duration of follow-up of 5.1 years. Radiographs made preoperatively and at the time of follow-up were evaluated for alignment in the coronal plane. RESULTS: The mean Knee Society knee score was 35 points before the arthroplasty and 84 points after the arthroplasty. The mean Knee Society function score was 49 points before the arthroplasty and 68 points after the arthroplasty. The mean interval between the femoral osteotomy and the total knee replacement was fourteen years (range, two to thirty-two years). A constrained prosthesis was required in five of the eleven knees. Two knees had an excellent result, five had a good result, and four had a fair result. The mean arc of motion improved from 81.8 degrees to 105.9 degrees. The mean radiographic alignment was 3.6 degrees of valgus (range, 7 degrees of varus to 18 degrees of valgus) before the arthroplasty and 3.3 degrees of valgus (range, 1 degrees of valgus to 6 degrees of valgus) at the time of the latest follow-up. There were no infections or wound complications. CONCLUSION: Total knee arthroplasty following distal femoral varus osteotomy decreases pain and improves knee function, but the procedure is technically demanding and is associated with inferior results when compared with those of primary arthroplasty performed in a patient without a prior femoral osteotomy. In the present series, the use of an intramedullary femoral alignment guide increased the tendency to place the femoral component in relative varus angulation (that is, in <5 degrees of valgus). We recommend checking the alignment of the femoral component with an extramedullary guide in knees that have had a previous distal femoral varus osteotomy.     

Does Tibial Slope Affect Perception of Coronal Alignment on a Standing Anteroposterior Radiograph?

BackgroundA standing anteroposterior (AP) radiograph is commonly used to evaluate coronal alignment following total knee arthroplasty (TKA). The impact of coronal alignment on TKA outcomes is controversial, perhaps due to variability in imaging and/or measurement technique. We sought to quantify the effect of image rotation and tibial slope on coronal alignment.MethodsUsing a standard extramedullary tibial alignment guide, 3 cadaver legs were cut to accept a tibial tray at 0°, 3°, and 7° of slope. A computed tomography scan of the entire tibia was obtained for each specimen to confirm neutral coronal alignment. Images were then obtained at progressive 10° intervals of internal and external rotation up to 40° maximum in each direction. Images were then randomized and 5 blinded TKA surgeons were asked to determine coronal alignment. Continuous data values were transformed to categorical data (neutral [0], valgus [L], and varus [R]).ResultsEach 10° interval of external rotation of a 7° sloped tibial cut (or relative internal rotation of a tibial component viewed in the AP plane) resulted in perception of an additional 0.75° of varus.ConclusionThe slope of the proximal tibia bone cut should be taken into account when measuring coronal alignment on a standing AP radiograph.     

Arthrodesis of the knee: experience with intramedullary nailing

Knee arthrodesis using an intramedullary nail has gained acceptance as treatment in difficult cases such as infection after total knee arthroplasty (TKA), neuropathic joint, and obesity. A retrospective review of 22 cases treated at our institution using an intramedullary nail for knee arthrodesis was performed. Deep infection after primary (11) or revision (6) TKA was the most common indication for this procedure. A long intramedullary nail was used in 3 cases, a long nail with a proximal interlocking screw was used in 6 cases, and a customized nail with a valgus bend and a proximal interlocking screw was used in 11 cases. A modular knee fusion nail was used in 1 case. Successful fusion occurred in all cases, although 4 patients required additional surgery. Average operative blood loss was 748 mL, and average time to union was 7 months. Shortening of the extremity averaged 3.2 cm. Tibiofemoral alignment was improved by using a customized valgus nail (average, 3.1 valgus; range, 1-5) when compared with a straight nail (average, 0.2 valgus; range, 3 varus to 3 valgus). No patient developed infection in the hip or ankle region as a result of the long intramedullary nail. Intramedullary nailing is an excellent technique for knee arthrodesis in difficult cases. A customized proximal interlocking nail with 5 degrees to 7 degrees of valgus and 5 degrees of anterior angulation improves tibiofemoral alignment and is straightforward to insert or extract should it be necessary. Stability and pain relief are rapid, and the fusion rate is maximized.     

The Coronal Plane High Tibial Osteotomy. Part 1: A Clinical and Radiographic Analysis of Intermediate Term Outcomes

The coronal plane high tibial osteotomy is a novel technique that is used to treat tibiofemoral malalignment. The authors hypothesize that the coronal plane high tibial osteotomy is (1) efficacious in treating both varus and valgus tibiofemoral malalignment; (2) does not alter the slope of the proximal tibia; and (3) does not alter the relationship between the patella and tibial tubercle. A retrospective review of 25 patients with tibiofemoral malalignment (19 varus/6 valgus) treated with a coronal plane osteotomy with a minimum of 2-year follow-up was performed. A Kaplan–Meyer survival curve was performed using knee arthroplasty and a Hospital for Special Surgery (HSS) knee score <70 as failure criteria. The Insall–Salvati ratio and the proximal tibial slope were measured. A p value of 0.05 was considered significant. At 60-month follow-up, knees with initial varus malalignment had an 84% survival rate using both knee arthroplasty and the HSS score as endpoints. Knees with initial valgus malalignment had an 84 and 60% survival rate using knee arthroplasty and the HSS score as endpoints, respectively. There was no statistically significant change in the Insall–Salvati ratio and proximal tibial slope after coronal plane osteotomy. The coronal plane osteotomy is efficacious in treating varus and valgus tibiofemoral malalignment and does not alter the patellar–tibial tubercle relationship or the posterior tibial slope [case series (level of evidence: IV)].     

Radiologic study of the accuracy of a tibial intramedullary cutting guide for knee arthroplasty

Twenty-one caucasian, adult cadaveric tibiac were prepared as for knee arthroplasty using an intramedullary cutting guide. The instrumentation was used to produce slots in the proximal tibia into which Kirschner wires were placed as radio-opaque markers for subsequent anteroposterior and lateral radiographs. The anatomic axis of the tibia and lines perpendicular to the wire markers were drawn on the radiographs and the angle between the two lines was measured to assess the accuracy of the cuts. Seventy-one percent of the tibial cuts were found to be within 2° of the anatomic axis on the anteroposterior radiograph (mean, 2.1°), while on the lateral radiograph, 81% of the cuts were within 2° (mean, 1.8°). There was a significant tendency to position the bone cuts in varus (P < .05), although this did not correlate with varus or valgus deformity of the bones. There was no consistent tendency to anterior or posterior tilt on the lateral radiograph (P > .05). The results compare favorably with those obtained from a specialist unit using an extramedullary alignment system. The authors conclude that the tibial intramedullary guide can lead to preparation of the proximal tibia for knee arthroplasty as accurately as the conventional extramedullary system.     

Optimizing patellofemoral tracking during total knee arthroplasty

Fifty-seven patients who underwent 65 primary TKAs between 1993-1994 were retrospectively studied to identify the technical challenges and pitfalls associated with patellar resurfacing and to improve patellar tracking during total knee arthroplasty (TKA). Average patient age was 69 years. All surgeries were performed by a single surgeon (J.N.I), and the same prosthesis was used in all patients. Intraoperatively, attention was paid to avoid femoral and tibial component malrotation and prevent overstuffing of the patellofemoral joint. Preoperative limb alignment was varus in 42 knees, neutral in 6 knees, and valgus in 17 knees. Average pre-resection patellar thickness measured 23.8 mm and post-resection thickness averaged 21.5 mm. No patella-prosthesis composite was thicker than the native patella. Two (3%) knees required a formal lateral release to improve patellar tracking at surgery. Average follow-up for 53 patients (61 knees) was 5 years. At latest follow-up, 4 (6%) patients reported mild anterior knee pain, 5 (7%) patients reported pain with stairs, and 2 (3%) patients had knee crepitus without pain. No dislocations or recurrent subluxations occurred. No patient required revision surgery for patellofemoral complication. Awareness of the anatomic variability, attention to component rotation, and restoration of the normal patellar height improves patellar tracking and minimizes patellofemoral instability following TKA.     

A reversed tibial flip autograft technique for correcting over-valgus knee after high tibial closing-wedge osteotomy in total knee arthroplasty

Excessive valgus deformity after a failed high tibial osteotomy presents problems for subsequent total knee arthroplasty because the proximal tibia is deformed, necessitating a much larger resection of bone from the medial aspect of the tibia. Other researchers have reported the tibial flip autograft technique to augment the tibial medial compartment to correct varus knee. We have modified this technique, which we call the reversed tibial flip autograft technique, for a patient with valgus knee after failed high tibial osteotomy. Clinical results were excellent, and no signs of loosening were apparent 2 years after surgery, suggesting that this technique is useful for management of tibial bone loss and correction of valgus angular deformity in total knee arthroplasty.     

Risk factors of post-operative malalignment in fixed-bearing medial unicompartmental knee arthroplasty

Purpose

The purpose of this study was to identify risk factors of post-operative malalignment in medial unicompartmental knee arthroplasty (UKA) using multivariate logistic regression.

Methods

We retrospectively enrolled 92 patients who had 127 medial UKAs. According to post-operative limb mechanical axis (hip-knee-ankle [HKA] angle), 127 enrolled knees were sorted into acceptable alignment with HKA angle within the conventional?±?3 degree range from a neutral alignment (n?=?73) and outlier with HKA angle outside?±?3 degree range (n?=?54) groups. Multivariate logistic regression was used to analyse risk factors including age, gender, body mass index, thickness of polyethylene tibial insert, pre-operative HKA angle, distal femoral varus angle (DFVA), femoral bowing angle (FBA), tibial bone varus angle (TBVA), mechanical distal femoral and proximal tibial angles, varus and valgus stress angles, size of femoral and tibial osteophytes, and femoral and tibial component alignment angles.

Results

Pre-operative DFVA, TBVA and valgus stress angle were identified as significant risk factors. As DFVA increased by one degree, malalignment was about 45 times probable (adjusted OR 44.871, 95 % CI 2.608–771.904). Shift of TBVA and valgus stress angle to a more varus direction were also significant risk factors (adjusted OR 13.001, 95 % CI 1.754–96.376 and adjusted OR 2.669, 95 % CI 1.054–6.760).

Conclusions

Attention should be given to the possibility of post-operative malalignment during medial UKA in patients with a greater varus angle in pre-operative DFVA, TBVA and valgus stress angle, especially with a greater varus DFVA, which was the strongest predictor for malalignment.

     

Effect of rotational malposition of the femoral component on knee stability kinematics after total knee arthroplasty

Excessive external rotation of the femoral component can cause an abnormally tight popliteus tendon complex, which induces loss of rotational laxity of the knee in the late phase of knee flexion after total knee arthroplasty. This study evaluated the effect of popliteus tendon release on rotational and varus—valgus laxity of implanted knees with an excessively externally rotated femoral component. Rotational and varus—valgus laxity was measured with a knee kinematics testing device before and after total knee arthroplasty. External rotational positions of the femoral component of 5° and 8° were compared, and the effects of popliteus tendon release on rotational and varus—valgus laxity were evaluated. To further investigate this question, the effect of a conforming articular design was compared with that of a flat tibial surface. External rotational position of 5° did not change rotational or varus—valgus laxity of the knee. With an 8° external rotational position, however, external rotational laxity significantly decreased in knees with a conforming surface at angles of 30°, 45°, 60°, and 90°. After popliteus tendon release, external rotational laxity significantly improved at 90° flexion and was identical to that of the normal knee. Internal rotational range was similar before and after popliteus tendon release. Popliteus tendon release did not affect the varus—valgus laxity (stability) with either articular surface.