Management of recurrent dislocation of the patella following total knee arthroplasty

Extensor Mechanism Centralization Using Autograft Hamstring for Laterally Dislocating Patella

Patellofemoral complications following total knee arthroplasty (TKA) are some of the most commonly cited complications in the literature, accounting for up to 50% of secondary procedures in the literature. Lateral dislocation of the patella, while rare, is one of many causes of extensor mechanism dysfunction. We sought to evaluate a novel patellar centralization procedure by comparing patients' pre- and postoperative clinical and radiographic data. A retrospective case-series study was performed on 12 patient knees (5 male and 7 female) presenting with ambulatory dysfunction due to laterally dislocating patella. All of the knees had component revision combined with hamstring autograft tendon weave and medial reefing of the retinaculum and vastus medialis. The results revealed reliable stabilization of the patella and improved extensor lag at a mean 2.2±2.2 years' short-term follow-up, which correlated with improved postoperative radiographic measurements. Range of motion in both flexion and extension was improved postoperatively. Improvements in radiographic measures of patellar tilt and patellar displacement were statistically significant, with reductions in the mean patellar tilt from 41.5°±25.9° to 3.9°±13.7° (P=.004), and in the mean patellar displacement from 2.8±2.1 cm to 0.8±0.9 cm (P=.012). Our study findings support the use of the extensor mechanism centralization procedure with autograft hamstring in management of laterally dislocating patella after TKA. [Orthopedics. 20XX;XX(X):xx-xx.].

Management of patella maltracking after total knee arthroplasty: a systematic review

PURPOSE

Patella maltracking is among the most frequent causes of poor outcomes and early failure after total knee arthroplasty (TKA), with an incidence that ranges from 1 to 20%. Even if there is agreement between authors regarding the preoperative and intraoperative management of patella maltracking in TKA, less clear are postoperative conducts. The purpose of this systematic review is to summarize and compare surgical techniques used to treat patella maltracking after TKA.

METHODS

A systematic review of the literature was performed with a primary search on Medline through PubMed. The PRISMA 2009 flowchart and checklist were used to edit the review. Screened studies had to provide clinical, functional and radiological results and complications of the proposed treatment to be included in the review.

RESULTS

A total of 21 articles were finally included. Three main types of surgical procedures and other minor techniques have been identified to manage patella maltracking after TKA. The choice of the proper technique to use in the specific case depends on several factors, first of all the malpositioning of the prosthetic components.

CONCLUSION

Patella maltracking after TKA represents a frequent and challenging problem for orthopedic surgeons. Treatments described in the literature are often able to correct an abnormal patellar tracking; nevertheless, authors report variable percentages of residual knee pain and dissatisfaction in re-treated patients. Therefore, it would be desirable to prevent the maltracking condition at the time of primary arthroplasty, using proper surgical precautions.

Can Patella Instability After Total Knee Arthroplasty be Treated With Medial Patellofemoral Ligament Reconstruction?

Background

The aim of this study was to describe outcomes of patients who had undergone medial patellofemoral ligament reconstruction (MPFLr) to treat patellofemoral instability (PFI) following total knee arthroplasty (TKA).

Material and methods

This is a retrospective case series of consecutive patients treated for PFI after TKA. Patients were included if they had radiographic documentation of patella dislocation or subluxation and component position was adequate. MPFLr was performed using a quadriceps tendon autograft. The graft was fixed with either an interference or additional suspensory fixation. A tibial tubercle osteotomy was performed in select indications. Patients were assessed with Kujala and International Knee Score (IKS) at a minimum 12-month follow-up and radiographically with plain radiographs.

Results

A total of 22 patients (23 procedures) were included. The mean follow-up period was 38 months (range 12-72). Average preoperative femoral component rotation on computed tomography was 0.10° external rotation (range 3° internal rotation to 3° external rotation). All patients had improved clinical and radiographic outcomes postoperatively. At the last follow-up, the mean IKS knee score was 77.6 ± 13.1, mean IKS function score was 75.2 ± 23.3, and mean Kujala score was 60.2/100 ± 10.9. There was 1 mechanical failure, which occurred following MPFLr with interference fixation. There were 6 complications (28.1%) postoperatively. Patients receiving double fixation of the MPFLr graft had higher clinical and radiographic scores; however, this difference was not statistically significant. MPFLr had a patella-lowering effect, 0.97 preoperatively to 0.74 postoperatively (P = .069).

Conclusion

MPFLr in appropriately selected patients is a satisfactory option to treat PFI following TKA.

Extensive Proximal Extensor Mechanism Realignment for Chronic Patella Dislocations in Revision Knee Arthroplasty: Surgical Technique

Patella dislocation after primary or revision total knee arthroplasty (TKA) is a major challenge in revision surgery. In practice, the main reason for patella maltracking and instability following TKA is malrotation of the femoral and/or tibial components. A number of soft tissue procedures, once component malrotation is corrected, have been described including proximal realignment, quadricepsplasty and distal realignment of patellar tendon with tibial tubercle osteotomy. Here, we describe our modified surgical technique in managing chronically dislocated patellae in knee arthroplasty which comprises of extensive lateral releases, vastus medialis obliquus (VMO) advancement and soft tissue reconstruction of the extensor mechanism with accompanying three case presentations achieving satisfactory clinical outcomes.

Revision total knee arthroplasty for patellar dislocation in patients with malrotated TKA components

PURPOSE

Patellar dislocation is a serious complication leading to patient morbidity following total knee arthroplasty (TKA). The cause can be multifactorial. Extensor mechanism imbalance may be present and result from technical errors such as malrotation of the implants. We sought to understand the reasons for post-arthroplasty patellar dislocation and the clinical outcomes of patients in whom it occurs.

METHODS

This is a retrospective cohort study assessing the outcomes of revision surgery for patellar dislocation in patients with component malrotation in both primary and revision TKAs. Patient demographics, dislocation etiology, presurgical deformity, intraoperation component position, complications, reoperation, and Knee Society Scores (KSS) were collected.

RESULTS

Twenty patients (21 knees) were identified. The average time from primary arthroplasty to onset of dislocation was 33.6 months (SD 44.4), and the average time from dislocation to revision was 3.38 months (SD 2.81). Seventeen knees (80.9%) had internal rotation of the tibial component and seven knees (33.3%) had combined internal rotation of both the femoral and tibial components. Fifteen knees (71.4%) were treated with a condylar constrained implant at the time of revision, and five knees were converted to a hinged prosthesis. The average follow-up time was 56 months. During this time, one patient (4.54%) had a recurrent dislocation episode, requiring further surgery. At final follow up, the mean KSS was 86.2.

CONCLUSION

Revision TKA following patellar dislocation for patients with malrotated components was associated with high success rates. After revision surgery, patients had a low recurrence of patellar dislocation, low complication rates, and excellent functional outcomes.

The Challenge of Managing the "Third-Space" in Total Knee Arthroplasty: Review of Current Concepts

Total knee arthroplasty (TKA) is the best treatment for advanced knee osteoarthritis and it has proven to be durable and effective. Anterior knee pain (AKP) is still one of the most frequent complications after TKA, but sometimes no recognized macroscopic causes can be found. The correct treatment of patella is considered the key for a proper management of AKP. The inclusion of patellar resurfacing during TKA has been described as a potential method for the reduction of AKP. After surgeons started to resurface the patella, new complications emerged, such as component failure, instability, fracture, tendon rupture, and soft tissue impingement. Patelloplasty has been proposed as a good alternative to resurfacing but whether or not to resurface the patella is still a controversial topic in the literature. Therefore, patellofemoral joint is a complex critical aspect in TKA and choosing between the several options of treatment of patella could not be sufficient. In this review, evidence-based studies do not succeed in resolving this difficult argument. The accurate management of the so-called “third space” should include an accurate assessment of cartilage layers, balance of soft tissue, preoperative anterior tracking, and positioning of the femoral and tibial components. In fact, the selection of suitable implants and adherence to proper surgical technique are the fundamental principles for the success of TKA.

[Causes and management of patellar instability after total knee replacement : Lateralization, subluxation and luxation]

BACKGROUND

Patellofemoral complications after total knee arthroplasty are responsible for a variety of surgical revisions.

OBJECTIVE

The causes of the various types of instability of the patella are listed in a differentiated way and the importance of clinical and imaging diagnostics as well as preventive strategies are elaborated.

MATERIAL AND METHODS

This article is based on a selective literature search in the PubMed database and on the long-standing experience of the author.

RESULTS

Besides postoperative genu valgum with malalignment of the extensor mechanisms, other risk factors for patellar maltracking are insufficiency of the medial retinaculum, weakening of the vastus medialis muscle, contracture of the quadriceps femoris or tractus iliotibialis muscle, residual valgus deformity after total knee replacement, femoral or tibial malrotation as well as malpositioning of the patella, inappropriate design of the prosthesis and asymmetrical resection of the patella. The causes with respect to incorrect component positioning, faulty preparation of the patella, leg malalignment, inappropriate design of the prosthesis and soft tissue imbalance have to be recognized in order to address the problem in a targeted way. The preferred method of choice in the case of patellofemoral instability after total knee replacement is normally surgery; however, the cause for the instability has to be identified and consequently corrected before surgery. Without a clearly identified cause surgical measures are unrewarding and almost regularly lead to an unsatisfactory outcome.

CONCLUSION

Patella maltracking after total knee arthroplasty is multifactorial and requires an accurate clarification. A surgical revision is only recommended in cases of clearly defined causes of pain or a clearly defined reason for patella malpositioning.

Review article: Patellar instability after total knee arthroplasty

Patellar instability after total knee arthroplasty (TKA) is a serious complication that impairs functional outcome and may lead to revision surgery. Its aetiology can be related to the surgical technique and component positioning, extensor mechanism imbalance, and other causes. After TKA, the presence of anterior knee pain, especially during stressful activities, is indicative of patellar instability. Diagnosis can be made by radiological evaluation of the patella position, alignment, and component fixation. Main treatment options include revision of the TKA components (in case of malposition) and lateral retinacular release with or without a proximal or distal realignment (in case of soft-tissue imbalance).

Fulkerson procedure for chronic patella component dislocation after total knee arthroplasty

Chronic patella component dislocation after primary knee arthroplasty can be a challenging problem. The purpose of this case series was to review our results of a chronic patella dislocation after total knee arthroplasty treated with a Fulkerson procedure (anteromedialization of the tibial tubercle). Five patients with an average age of 68.8 years (range, 60-76 years) underwent a Fulkerson procedure to restore extensor mechanism alignment. The tibial tubercle osteotomy was secured with lag screws with an average medialization of approximately 1.5 cm. The average preoperative Knee Society score was 70.5 points that improved to 85 points postoperatively. The average knee flexion was 93 degrees preoperatively that improved to 101 degrees postoperatively. Adequate patellofemoral alignment was achieved in all patients along with union of the tibial tubercle osteotomy site. The Fulkerson procedure appears to be an excellent treatment option in patients with a chronically dislocated patella component after total knee arthroplasty.

Gait during hydrokinesitherapy following total knee arthroplasty

PURPOSE

To obtain gait parameters during hydrotherapy (HT) in patients who were referred for rehabilitation after primary total knee arthroplasty (TKA).

METHOD

The study had a cohort prospective design. Patients who had undergone TKA followed a HT rehabilitation programme. Twenty-two consecutive patients were enrolled. Four of them dropped out for various reasons, independently of HT. Therefore 18 patients could be evaluated (5 men and 13 women). Eighteen age-matched healthy volunteers were the control subjects. Nine patients had a right TKA and nine a left TKA. On the average HT duration was 18.4 days (SD 1.4).

RESULTS

The patients presented with a mean speed of 912 (SD 275) meters per hour (m/h) at the baseline. At the last session the mean speed was 1330 (SD 416) m/h. The mean stance duration was 1.75 s (SD 0.34) on the operated side and 1.83 s (SD 0.41) on the non-operated side. By contrast, the mean swing duration was 1.10 s (SD 0.25) on the operated side and 1.13 s (SD 0.34) on the non-operated side. The step duration was the same on both sides. At the beginning of HT the mean stance/swing ratio was 1.94 on the operated side, whereas it was 1.77 on the non-operated side. In the controls the ratio was 1.46. At the beginning the mean stride length was 0.526 m (SD 0.147) and the value became 0.556 (SD 0.138) after 18 training sessions. At the individual level, recovery occurred in a non-linear fashion (Best Fitting, 7th-grade Fourier finite series).

CONCLUSIONS

The study design permits accurate definition of stride parameters during rehabilitation which allows optimization of the programme. Increase in speed and regain of balance are the main targets of a HT programme and are monitored on a daily basis.

The management of patients with painful total knee replacement

The management of patients with a painful total knee replacement requires careful assessment and a stepwise approach in order to diagnose the underlying pathology accurately. The management should include a multidisciplinary approach to the patient's pain as well as addressing the underlying aetiology. Pain should be treated with appropriate analgesia, according to the analgesic ladder of the World Health Organisation. Special measures should be taken to identify and to treat any neuropathic pain. There are a number of intrinsic and extrinsic causes of a painful knee replacement which should be identified and treated early. Patients with unexplained pain and without any recognised pathology should be treated conservatively since they may improve over a period of time and rarely do so after a revision operation.

How to address the patella in revision total knee arthroplasty

Patellar issues need to be carefully addressed during any revision TKA and the surgeon often faces the question of what to do with the patella at the time of revision. The choice of treatment is often made by balancing what is technically feasible with the risk of potential complications and takes into account the reason for the revision, the type of implant (i.e., metal-backing or all-polyethylene), the duration of implantation, the fixation, the stability, the sterilization technique, the wear, the presence of osteolysis, the compatibility with the femoral component, and most importantly the remaining bone stock. The various treatment options then include retention of the patellar component, revision of the patellar component, removal of the component with retention of the patellar bony shell (patelloplasty or resection arthroplasty), excision of the patella (partial or total patellectomy), secondary resurfacing, and reconstruction/augmentation of the patellar bone stock. Isolated patellar revision is associated with a high complication rate and recurrent failure when poor patellar tracking, incongruent designs and malalignment of the femoral and tibial components exist. Retention of a well-fixed all-PE (non-oxidized) patella is advocated where possible and revision of metal-backed patella is recommended (unless well fixed with poor bone stock). In the situation of a deficient patella, patelloplasty, augmentation procedures and very rarely patellectomy are other viable options.

Patellofemoral instability after total knee arthroplasty

Despite advances in surgical technique and implant design, complications involving the extensor mechanism and patellofemoral joint after total knee arthroplasty (TKA) continue to be the most common cause of pain and the most commonly cited reason for revision TKA surgery. A thorough understanding of the etiologies of patellofemoral instability, careful preoperative planning, and meticulous surgical techniques will optimize clinical outcome. Evaluation of patellofemoral stability should begin in the operating room. Postoperatively, thorough history, physical examination, and dedicated radiographic studies should be obtained. Computed tomography scan is the most accurate and reliable way to assess component positioning. Treatment of patellofemoral instability is directed by its etiology. Revision of one or both components is indicated if malpositioning is present. If the components are determined to be in satisfactory positions, soft tissue procedures can be pursued. Future advancements in prosthetic design and the routine use of computer-assisted navigation systems will minimize patellofemoral instability.

LEVEL OF EVIDENCE

Therapeutic study, Level V (expert opinion). See the Guidelines for Authors for a complete description of levels of evidence.

The long-term results of a metal-backed mobile bearing patella

Enthusiasm for metal-backed patella has waned because of the high incidence of complications. Considering that perhaps all metal-backed patellae may not be the same, 256 primary consecutive metal-backed mobile bearing TKAs done between May 1985 and January 1989 were retrospectively reviewed to evaluate the results of a unique mobile bearing metal-backed patella. There were four complications (1.6%). Three patella were revised for polyethylene complications and one well-functioning component was removed at the time of revision of the tibial polyethylene to facilitate range of motion and wound closure. No patella was revised for loosening, subluxation, or dislocation. Our results show that all metal-backed patella are not the same and that compared with the high incidence of failure of fixed bearing metal-backed patellae, the use of the anatomic mobile bearing metal-backed patella can produce excellent, durable long-term clinical and radiographic results with a low incidence (1.6%) of complications. Life table survivorship using revision for any reason as the end point was 97% (95% confidence interval, 93%-100%) at a maximum of 19 years.

LEVEL OF EVIDENCE

Therapeutic study, Level IV (case series--no, or historical control group). See the Guidelines for Authors for a complete description of levels of evidence.

Anatomic dimensions of the patella measured during total knee arthroplasty

The anatomic measurements of 92 patellae with normal underlying bony structure were studied during total knee arthroplasty before and after resection of the articular surface. The articular surface of the patella was found to have an oval shape with a width-to-height ratio (46 x 36 mm) of 1.30. The dome was 4.8 mm high and displaced medially 3.6 mm. The medial facet was slightly thicker than the lateral facet (18 vs 17 mm). The lateral facet is 25% wider than the medial facet. Coverage provided by oval patellar prostheses was significantly better than with round prostheses. The patellae in women were significantly smaller than in men. Size differences and deformity need to be taken into account when the patella is prepared for resurfacing. It is recommended that the bony resection should be no greater than one third of the maximum patellar thickness to avoid alteration of normal bony structure. Key words: patella, total knee arthroplasty, anatomy.

Revision surgery for patellar dislocation after primary total knee arthroplasty

This study evaluated risk factors for patellar dislocation after primary total knee arthroplasty and determined functional outcomes in patients following revision. Thirty-nine knees in 39 patients averaging 68 years (range, 27-91 years) at the time of revision were evaluated at a mean of 3.2 years (range, 2-7 years). Mean Knee Society and Function scores significantly improved from 34 and 35 to 77 and 54, respectively. Patellar dislocation most commonly resulted from errors in technique such as soft-tissue imbalance and malaligned components that led to poor tracking of the patella. Patellar tracking only improved after soft-tissue realignment in combination with revision of malaligned or loose components. Although revision significantly improved active knee extension and Knee Scores, two thirds of the patients had residual disabilities and pain.

Patellar options in revision total knee arthroplasty

There are numerous options that need to be considered by the surgeon at the time of revision total knee arthroplasty (TKA). One needs to consider the reason for the revision, the type of patella in place, and the length of time the patella has been in place. The surgeon also needs to consider the status of the patellar bone stock, the stability of the patellar component (well-fixed or loose), and the component type (cemented or metal-backed). Assuming that the existing prosthesis is not metal-backed and has minimal PE wear, then it is preferable to retain a well-fixed all-PE cemented patellar button. However, if the button is metal-backed, then it probably is best to remove the button and replace it with an all-PE domed patellar component. Assuming more than 8 mm of patellar bone stock is remaining, it usually is best to cement an all-PE dome-shaped patella. However, if less than 8 mm is remaining, then that patient can be left with a patelloplasty, recognizing that this individual is going to continue with a high likelihood of anterior knee pain, subluxation, and poor functional results. In that situation, it may be preferable to consider a bone stock augmentation.

The unstable patella after total knee arthroplasty: etiology, prevention, and management

In total knee arthroplasty, most complications related to the extensor mechanism are caused by patellar maltracking or instability. Patellar maltracking may result from component malpositioning and limb malalignment, prosthetic design, improper patellar preparation, or soft-tissue imbalance. Patellofemoral instability likely results most frequently from internal malrotation of the femoral or tibial components. Although a patellofemoral radiograph may display the lateral subluxation of the patella, only computed tomography can quantify rotational malalignment of the femoral or tibial component. Nonsurgical treatment is generally unsuccessful; major malposition of components is best managed by implant revision. In the absence of component malposition, proximal realignments (lateral patellar retinacular release with lateral advancement of the vastus medialis obliquus muscle) or tibial tubercle transfers have been used. Surgical procedures on the patellar tendon itself may risk rupture of the extensor mechanism.

Extensor mechanism failure associated with total knee arthroplasty: prevention and management

Extensor mechanism complications are the most commonly reported reasons for revision surgery after total knee arthroplasty and are a frequent source of postoperative morbidity. Patellofemoral instability is the most commonly reported extensor mechanism complication and has multiple etiologies, including prosthetic malalignment and soft-tissue imbabalce. Patellar fracture or rupture of either the quadriceps or patellar tendon can cause catastrophic disruption of the extensor mechanism. Although some stable fractures can be successfully managed nonsurgically, displaced fractures or tendon rupture often lead to poor results. Other complications include patellar clunk and soft-tissue adhesions, prosthetic wear or loosening, and osteonecrosis. Increased understanding of implant alignment, rotation, and soft-tissue balance, as well as improved design of the trochlear groove of femoral implants and patellar components, has resulted in a decline in extensor mechanism complications. Appropriate prosthetic selection and meticulous surgical technique remain the keys to avoiding unsatisfactory results and revision surgery.

The consequences of lateral release in total knee replacement: a review of over 1000 knees with follow up between 5 and 11 years

BACKGROUND

The relationship between lateral release in total knee arthroplasty and subsequent patello-femoral problems is contentious. Variable rates of instability, patella fracture and other complications have been demonstrated after lateral release. Significant measures have been taken by some surgeons to avoid a lateral release. We wished to determine whether lateral release was detrimental or beneficial in terms of mid- to long- term patellofemoral problems.

METHODS

We examined 1071 total knee arthroplasties with a follow-up of 5 to 11 years to determine the longer-term consequences of lateral release. Lateral release was performed as clinically indicated after a 'no thumbs' assessment in 51% of cases. The knees requiring a lateral release had lower pre-operative Hospital for Special Surgery (HSS) scores and demonstrated a greater improvement in post-operative HSS scores.

RESULTS

The difference in HSS scores, between the groups, was significantly less post-operatively than prior to surgery. Overall, we had a high incidence of lateral release (51%), but low fracture rate (1.2%), and very low instability rate (0.6%). Only three surgeries were required for patello-femoral problems.

CONCLUSION

This study suggests that any negative consequences of lateral release are minimal and we recommend lateral release continue to be performed as clinically indicated.

The effect of surgical approaches and tourniquet application on patellofemoral tracking in total knee arthroplasty

The purpose of this study was to assess the influences of surgical approaches and tourniquet application on the lateral retinacular tension (LRT). Single-setting bilateral total knee arthroplasty was performed in 10 patients, and the medial parapatellar and midvastus approaches were randomly performed on each knee using tourniquet application. The LRT was measured using the buckle transducer before and after each approach. Next, the tourniquet was deflated and the measurement was repeated. After the parapatellar approach, LRT was significantly decreased. Conversely, no significant change was seen after the midvastus approach with the tourniquet inflated. However, in the midvastus approach, LRT was significantly decreased after tourniquet deflation. We concluded that both the parapatellar and midvastus approaches influence patellar tracking and LRT.

The effect of femoral component rotation and asymmetry in total knee replacements

Between April 1999 and February 2000, femoral component rotation and asymmetry (universal versus anatomic) were studied in a prospective randomized control trial in 101 consecutive patients undergoing total knee replacement. Patients were randomly assigned to four groups. The same surgical technique was used in all patients except for femoral component symmetry and rotational alignment. Universal femoral components provide a cheaper and equally reliable solution compared to anatomic compo nents. External rotation of the femoral component or using an anatomic femoral component did not statistically reduce the need for lateral release or improve patellar tracking.

The clinical history of mobile-bearing patella components in total knee arthroplasty

Two hundred fifty-six primary cementless meniscal-bearing total knee arthroplasties were performed between May 1985 and January 1989. All knees were replaced with a low contact stress metal-backed anatomic mobile patella. The average patient follow-up was 11.5 years. No patellae were revised for failure of fixation and no dislocations or subluxations were reported. One patella was revised for polyethylene wear, and one well-functioning component was removed at the time of revision to facilitate range of motion and wound closure. The survival estimate at 12 years was 99.5%. Compared to the high incidence of failure of metal-backed fixed-bearing patellae components, the anatomic rotating patella provides durable long-term results with a low incidence of complications.

Aseptic complications after total knee arthroplasty

Aseptic complications after total knee arthroplasty are occurring less frequently than they did one or two decades ago. This is related in part to technical advancements, design improvements, and changes in perioperative management. Extensor mechanism dysfunction is the most frequent complication and the most commonly cited reason for secondary surgery after total knee arthroplasty. Mechanical wear, tibiofemoral instability, periprosthetic fracture, thromboembolic disease, compromised wound healing, neurovascular problems, and stiffness are less common, but nevertheless troublesome, sources of dysfunction after total knee arthroplasty. Complications compromise outcomes, and the most effective way of dealing with complications is prevention.

Current concepts review: symmetry versus asymmetry in the design of total knee femoral components--an unresolved controversy

Despite the excellent success of earlier total knee replacement designs such as the Total Condylar Knee (Johnson & Johnson, Raynham, MA), which had a symmetrical femoral component, the majority of modern designs feature a more anatomic and asymmetric femoral prosthesis. A raised lateral phalange, an angled trochlear groove, or both are thought to improve patellar tracking. Laboratory studies, however, suggest that surgical technique may be the dominant factor in determining patellofemoral kinematics. Component design has not been proven to be significant. A prosthesis with asymmetric femoral components may cost more. The literature reviewed in this article finds no advantage to the use of asymmetric versus symmetrical femoral components in total knee replacement.

Influence of surgical approach on lateral retinacular releases in total knee arthroplasty

The rate of lateral retinacular releases in 2 groups of patients who underwent knee surgery performed by the senior author is compared and the factors that contribute to these differing rates are discussed. The first group of subjects consists of 88 patients who had total knee arthroplasties performed with a standard medial parapatellar approach between August 1987 and August 1988. The second group is comprised of 88 patients who had total knee arthroplasties through a midvastus surgical arthrotomy that splits the fibers of the vastus medialis muscle. This method is used by the senior author for all primary total knee arthroplasties. Lateral retinacular releases were performed in 50% of the cases in the medial parapatellar group versus only 3% of the cases in the midvastus group. Patellofemoral instability occurs as a consequence of incising the quadriceps tendon in the medial parapatellar approach and results in the need to perform lateral retinacular releases. The reduction in lateral retinacular releases is attributed to the fact that the midvastus approach leaves the connection of the vastus medialis to the quadriceps tendon intact.

Component design affecting patellofemoral complications after total knee arthroplasty

Three hundred one primary cemented total knee arthroplasties were performed in 289 patients. Two different prostheses were used; 148 knees received the Miller-Galante I prosthesis and 153 knees received the Press Fit Condylar prosthesis. Minimum followup was 2 years. The groups were similar in all parameters both preoperatively and postoperatively, with the exception of the patellofemoral complication rate. Knees that were implanted with the Miller-Galante I prosthesis experienced a complication rate of 10.1%, while those with the Press Fit Condylar prosthesis experienced a complication rate of 0.7%. The distinct difference in the patellofemoral complication rate may be due to the differences in design of the femoral component. Features that may have contributed to increased patellofemoral morbidity included a short, narrow anterior flange; a shallow patellar groove; and an abrupt anterior to distal transition with a smaller radius of curvature. Because subtle design difference can have a profound effect on clinical outcome, long term evaluation of new designs should be completed before widespread use. The clinician also should be aware of the desirable design features when choosing a component.

Intercondylar distal femoral fracture. An unreported complication of posterior-stabilized total knee arthroplasty

In an attempt to study the incidence of intraoperative femoral intercondylar fractures, two large series of posterior-stabilized total knee arthroplasty (TKA) systems were reviewed. Eight hundred ninety-eight nonconsecutive primary posterior-stabilized TKAs were compared with a second nonconsecutive series of 532 posterior-stabilized TKAs. Unique to the secondary TKA system is an intercondylar sizing guide to aid in verification of the intercondylar resection size. In the initial series, 40 distal femoral intercondylar fractures were noted (rate = 1:22; nondisplaced, 35; displaced, 5). In the secondary series, one displaced distal femoral intercondylar fracture occurred (rate = 1;532). The difference in the rate of fracture between the two populations was statistically significant (P<.001). Intraoperative distal femoral intercondylar fracture represents a potential complication of TKA and can be avoided with careful resection technique and size verification. No change in the postoperative rehabilitation program is required, however, for those patients identified with nondisplaced and intraoperative-stabilized displaced distal femoral intercondylar fractures.

Patellofemoral Pain After Total Knee Arthroplasty

The incidence of patellofemoral complications after total knee arthroplasty has been reported to range from 2% to 7%. Such complications include pain, sub-luxation, dislocation, loosening, and wear. Usually these complications are attrib-utable to prosthetic design or surgical technique. Today, it is understood that patellofemoral prostheses must have a degree of congruence; must allow smooth, not abrupt, motion; and must restore a relatively normal size relationship between the patella and the femur. Surgical technique requires strict attention to (1) restoration of the patellofemoral spacing while avoiding "overstuffing" of the patellofemoral compartment; (2) accurate superior and medial positioning of the patellar component; (3) restoration of the rotational alignment of the femoral and tibial components; and (4) appropriate balancing of the patellofemoral soft tissues.

Clinical comparison of the Miller Galante I and AMK total knee systems

One hundred patients with primary osteoarthritis of the knee were prospectively randomized to assess the clinical outcome between two contemporary knee designs, namely the Anatomic Modular Knee (AMK, DePuy, Warsaw, IN) and the Miller Galante I (MG I, Zimmer, Warsaw, IN). In addition, patients were stratified by surgeon. While the clinical outcome measured by the Hospital for Special Surgery knee scores was similar for both groups, there was a difference in the number of complications requiring further surgery. Extensor mechanism complications requiring further surgery occurred in four patients (3 MG I and 1 AMK); three patients in the MG I group required a distal realignment procedure for patellar dislocation, while none of the AMK patients had this complication. There was, however, one patellar fracture in the AMK group that required an open reduction. The authors postulate that the major difference contributing to patellofemoral complications relates to the patellofemoral design and patellar tracking, with the more anatomic AMK femoral component having better patellar tracking and stability clinically.