Long-term complications after total knee arthroplasty with or without resurfacing of the patella

Dynamic in vitro measurement of patellar movement after total knee arthroplasty: an in vitro study

BACKGROUND

Changing the kinematic behaviour of patellar movement could be one of the reasons for anterior knee pain after implantation of a total knee arthroplasty (TKA). The aim of the current study was to measure the potential influence on patellar kinematics of patellar resurfacing during TKA.

METHODS

Patellar movement before and after TKA with and without patellar resurfacing was measured under dynamic conditions in an in vitro cadaver simulation. Physiologic Musculus quadriceps forces were applied to five physiologic human knee specimens undergoing simulated isokinetic extension motions, patellar movement was measured using an ultrasonic measurement system. Thereafter, the Interax I.S.A.-prosthesis system was implanted without and with resurfacing the patella, and patellar movement was again measured.

RESULTS

The physiologic patella center moved on a semilunar path up to 6.4 mm (SD 6.4 mm) medially during extension. After TKA, the unresurfaced patella showed significantly less medial translation (p = 0.04) than the resurfaced patella. Subsequent resurfacing of the patella then resulted in a return to mediolateral positioning of the patella similar to the physiological case, whereas the resurfaced patella tilted up to twice as much as physiologic.

CONCLUSION

The results of this study suggest that resurfacing of the patella during TKA can result in a restoration of the physiologic mediolateral shift of the patellofemoral joint while angulation of the patella remains unphysiologic.

Positionnement patellaire et voie latérale dans l’arthroplastie totale pour gonarthrose avec arthrose fémoro-patellaire latéralisée

PURPOSE OF THE STUDY

Patellar malposition is a well-recognized patellar complication after total knee arthroplasty. Such residual malposition is particularly frequent when the knee presents lateral femoropatellar arthrosis. We compared the radiological position of the patella after total knee arthroplasty in degenerative knees with lateral femoropatellar arthrosis performed via a medial or lateral approach with elevation of the anterior tibial tuberosity.

MATERIAL AND METHODS

Twenty-six total knee arthroplasties were reviewed retrospectively. Thirteen prostheses had been inserted via a medial approach and thirteen via a lateral approach. A posterior stabilized implant was used with an original technique for insertion of the patellar implant. The only difference between the groups was the approach. In the "lateral" group, the lateral approach was used to raise the tibial tuberosity and perform lateral marginal patellectomy. The tibial tuberosity was reinserted in all cases without transposition. Preoperative and 3-month postoperative radiographs (weight-bearing, AP, lateral, femoropatellar 30 degrees flexion) were reviewed. Preoperative patellar displacement was at least 5 mm. There was no difference between the two groups for age, gender, weight, height, joint motion, pre- and postoperative mechanical alignment (HKA), or preoperative patellar gliding (7.6 mm in the "medial" group and 9.7 mm in the "lateral" group).

RESULTS

Recurrent patellar dislocation occurred in one patient in the "medial" group and one patient in the "lateral" group had an anterior impaction of the tibial plateau following a fall. Patellar gliding was corrected in both groups: 0.7 +/- 1.8 mm in the "medial group" and 0.0 +/- 0 in the lateral group (p > 0.05). Residual patellar tilt was +4.2 +/- 3 degrees in the medial group (lateral tilt) and -3.3 +/- 5.4 degrees in the lateral group (medial tilt) (p = 0.003).

DISCUSSION

Pateller gliding was corrected irrespective of the approach. Conversely, the medial approach did not allow effective correction of patellar tilt. The lateral approach with elevation of the anterior tibial tuberosity did not increase morbidity compared with the medial approach. It enabled avoiding residual lateral patellar tilt which can be a source of patellar complications. We prefer this approach for arthroplasty on degenerated knees with lateral femoropatellar arthrosis.

Patellar resection during total knee arthroplasty: effect on bone strain and fracture risk

Patellae in small knees, or after severe patellar erosion, may be vulnerable to fracture after resection during arthroplasty. The patellar remnant may be thin, while the polyethylene component has a standard thickness. Anterior patellar bone strain was measured in cadaver knees loaded via the quadriceps, from 0 to 90 degrees flexion, with the patella intact, and after resections to 16, 13 and 11 mm thick and replacement by an 8-mm-thick polyethylene component. Strain increased significantly with knee flexion with constant 500 N quadriceps tension. Resection caused significant changes from intact values in knee flexion and extension and no significant effect at 30 degrees flexion. In flexion, bending caused the anterior surface to become more convex, with high tensile bone strains. In extension, resection caused negative anterior strains, representing bending in the opposite direction, with large tensile strains on the cut posterior surface. For normal activities, such as rising from a chair (1.8 kN quadriceps tension) the patella appears safe against fracture with a minimal resection to 16 mm thick. An eroded patella resected to 11 mm thickness may be at risk of fracture with that loading.

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.

Implant survivorship and complication rates after total knee arthroplasty with a third-generation cemented system: 5 to 8 years followup

We evaluated implant survivorship, reoperation rates, and complication rates of a group of patients who had total knee arthroplasty with a third-generation cemented prosthetic device using cruciate-retaining and posterior-stabilized designs at 5 to 8 years followup. Three hundred thirty-four consecutive primary total knee arthroplasties (186 cruciate retaining and 148 posterior stabilized) were done in 287 patients at our institution during a 2-year period. Kaplan Meier survivorship using revision for any reason and revision for aseptic loosening as endpoints were 95.9% and 99.5% respectively at 8 years. Nine patients (four with cruciate-retaining total knee arthroplasties, five with posterior-stabilized total knee arthroplasties; 3.1%) had reoperations for any reason. No patients had reoperation for problems related to the patellofemoral joint. Thirty-two patients (11.1%) had intraoperative or postoperative complications. There were no differences in any of the outcomes analyzed between patients who had cruciate-retaining or posterior-stabilized total knee replacements. Our results show that with appropriate patient selection and meticulous attention to surgical technique, excellent clinical and radiographic results can be achieved with a third-generation total knee arthroplasty system at intermediate followup.

LEVEL OF EVIDENCE

Therapeutic study, Level III-2 (retrospective cohort study).

Patellar resurfacing in total knee arthroplasty for osteoarthritis: a systematic review

A systematic review was performed to determine the advantages and disadvantages of patellar resurfacing during total knee replacement for osteoarthritis. Three randomised controlled studies were analysed. These studies recruited 302 knees and 235 knees (78%) were reviewed at least 5 years postoperatively (range 5 10 years). Patients undergoing patellar resurfacing received a cemented all polyethylene patella component. A patelloplasty was performed in some of the unresurfaced knees. For the dichotomous data, odds ratios and 95% confidence intervals were calculated. Each outcome measure tested was assessed for heterogeneity using the Cochran Q test. If significant heterogeneity was present (p < 0.10), data from the studies were not combined. If there was no significant heterogeneity, a combined odds ratio was calculated using a fixed effects model and a Z test was performed to test the overall effect. Reoperation for patellofemoral problems was significantly more likely in the unresurfaced group (p = 0.003). The overall rate for reoperation for a patellofemoral problem was 0.7% in the resurfaced group and 11% in the unresurfaced group. Study data on anterior knee pain could not be analysed together as there was significant heterogeneity. There was no difference between the two groups in terms of revision. This study found no mid- to long-term benefit to leaving the patella unresurfaced.

The consequences of not resurfacing the patella

The decision of whether to resurface the patella during total knee arthroplasty remains controversial. In this study, a meta-analysis of national joint replacement registry data, bilateral total knee replacement studies, selective resurfacing reports, and randomized clinical trials was done Although the evidence seems to support patellar resurfacing, this issue remains inconclusive because of problems generalizing from one implant to another and the short-term nature of available studies. Based on existing data, patellar resurfacing seems reasonable in most total knee replacements. Not resurfacing the patella might be considered in selected younger patients (<60 years) with mild or no patellar arthritis, a well-tracking extensor mechanism, and particularly if a patella-friendly femoral component is used.

Lateral retinacular release as a function of femoral component rotation in total knee arthroplasty

A consensus exists in the orthopaedic community that proper rotational placement of components may reduce the need for lateral release. This study compares the rates and results of lateral release before and after femoral component placement was defined by the transepicondylar axis (TEA). Between 1990 and 1991, 104 primary total knee arthroplasties (TKA) were reviewed during which equal amounts of bone from the posterior femoral condyles were removed. In this group, the lateral release incidence was 24% for varus deformities and 33% for valgus deformities. When the femoral component was externally rotated approximating the TEA, a review of 246 primary TKAs performed between 1998 and 1999 showed lateral release rates of 7% in varus deformities and 29% in valgus deformities. This study documents the statistically significant decline in the lateral release rate with external rotation of the femoral component during TKA in varus deformities (P<.0001), and a decreasing trend in valgus knees (P =.09).

Long-term changes of the nonresurfaced patella after total knee arthroplasty

BACKGROUND

The most common complications of total knee arthroplasty involve the patellofemoral joint. However, the long-term fate of the nonresurfaced patella after total knee arthroplasty has seldom been reported. The purpose of this study was to evaluate the long-term changes of the nonresurfaced patella after total knee arthroplasty.

METHODS

We retrospectively evaluated the nonresurfaced patella in 227 knees (181 patients) at an average of 8.5 years after total knee arthroplasty. Functional results were correlated with radiographic changes, and risk factors leading to abnormal changes of the patella were analyzed.

RESULTS

Preoperatively, 186 (82%) of the patellae tracked centrally, thirty-nine (17%) displaced or tilted laterally, and two (1%) subluxated laterally. At the time of the latest follow-up, 133 (59%) of the patellae still tracked centrally with preservation of the cartilage thickness, fifteen (7%) showed early lateral tilt, sixty-eight (30%) had progressive loss of lateral cartilage thickness with lateral tilt and/or displacement, seven (3%) had progressed to lateral subluxation, and four (2%) tilted medially. An abnormal patellofemoral joint did not affect the knee and functional scores (p = 0.90 and 0.89, respectively). However, symptoms such as difficulty rising from a chair or reluctance to use the involved lower limb while climbing stairs were noted. Preoperative patellar maltracking was identified as the only risk factor leading to postoperative patellar abnormalities (relative risk, 2.7; 95% confidence interval, 2.21 to 3.30; p = 0.003).

CONCLUSIONS

At the time of follow-up, at an average of 8.5 years, patellar tracking and the patellofemoral joint remained normal after approximately 60% of the total knee arthroplasties performed without resurfacing of the patella. Progressive degenerative changes of the nonresurfaced patella (mainly on the lateral facet) and patellar maltracking were the most common abnormal radiographic changes. Patients with preoperative patellar maltracking were at risk for the development of these changes and clinical symptoms. Resurfacing of the patella during total knee arthroplasty may benefit such patients.

Secondary patellar resurfacing in total knee arthroplasty: results of multivariate analysis in two case-matched groups

Although patellofemoral symptoms after patellar-retaining knee arthroplasty are common, no evidence has been published in the literature on the potential benefit from patellar resurfacing at a later stage. This study evaluates the effect of secondary (delayed) patellar resurfacing using comparisons between 2 case-matched groups of patients with primary and secondary patellar resurfacing. Furthermore, multivariate statistical methods were applied to study factors that may influence the final outcome. Our results suggest that although significant clinical improvement was seen after delayed patella resurfacing, the outcome of secondary patellar resurfacing is inferior to that expected for a similar group of patients with primary resurfacing. Furthermore, the timing (delay period) of the secondary resurfacing procedure appears to negatively affect the final outcome. This suggests that secondary patellar resurfacing, when indicated, should be considered at an early stage.

15-year follow-up study of total knee arthroplasty in patients with rheumatoid arthritis

In 25 patients with rheumatoid arthritis, 36 cases of cemented Kinematic total knee arthroplasty were reviewed clinically and radiographically at 13 to 19 years after surgery. The mean age at the time of surgery was 51.6 +/- 8.9 years. According to the follow-up results evaluated with the Hospital for Special Surgery knee scoring system, 28 knees (77.7%) were classified as good or excellent. The mean flexion angle at follow-up evaluation was 99 degrees +/- 24 degrees (10 degrees -140 degrees ). At the tibial or femoral bone-cement interfaces, a radiolucent line was seen in 10 of 36 knees (27.8%) at follow-up evaluation. The survival rate of prostheses with revision as the endpoint was estimated to be 93.7% at 15 years. Kinematic total knee arthroplasty in rheumatoid arthritis patients provided a good long-term outcome.

Bilateral patellar component dissociation in a patient with total knee arthroplasties

We present a case of bilateral patellar component dissociation 6 years after bilateral total knee arthroplasty. The patient had undergone arthroscopic lateral releases bilaterally for patellar maltracking. After repetitive trauma, the patient experienced patellar component dissociation, which was treated arthroscopically by removing the patellar components and leaving the patellae unresurfaced. The patient's symptoms improved substantially. Our case highlights certain features of the etiology as well as the management of patellar component dissociation in the total knee arthroplasty, showing the important role of arthroscopy.

Excisional arthroplasty for patellar loosening in total knee arthroplasty

Four thousand two hundred eighty-seven cases of Anatomic Graduated Components total knee replacements with a cemented, single-peg, all-polyethylene patellar component were performed at our institution over the past 15 years. One hundred eighty cases of patellar component loosening were found. Eleven knees (0.3%) in 11 patients required isolated patellar component reoperation. In all cases, the patellar component was excised and not reimplanted. The average follow-up for the 11 patients was 2.2 years. Five had a complete minimum follow-up of 2 years following reoperation. Pain and function were improved. Complications included infection in 3 knees and extensor lag in 1 knee. Because of the complication rate associated with isolated patellar component excision caused by a loose patellar component, we recommend surgical removal of the patellar component only in cases of severe pain and/or prominence of the component.

Resurfacing versus not resurfacing the patella in total knee arthroplasty: 8- to 10-year results

Patellar resurfacing in total knee arthroplasty is a topic debated in the literature. Concerns include fracture, dislocation, loosening, and extensor mechanism injury. Residual anterior knee pain has been reported when the patella is not resurfaced. One hundred patients with osteoarthritic knees were prospectively randomized to either have their patella resurfaced or left not resurfaced. All patients were treated with a single prosthesis that featured an anatomically designed patellofemoral articulation (Anatomic Medullary Knee, DePuy, Warsaw, IN) Two patients in the unresurfaced group and one in the resurfaced group required repeat surgery for patellofemoral complications. At 8- to 10-year follow-up evaluations, Knee Society Clinical Ratings scores were not different between the 2 groups. Rates of anterior knee pain with walking and stair climbing were significantly less in the resurfaced group. Eighty percent of patients with a resurfaced patella were extremely satisfied with their total knee arthroplasty versus 48% without patellar resurfacing. When satisfied and extremely satisfied patients were grouped together, there was no difference between the 2 groups.

Routine patellar resurfacing: a viable option

The literature on routine patellar resurfacing documents that the rate of anterior knee pain after TKA is the same whether the patella is resurfaced or unresurfaced. The complication rate is different in these groups. In patients in whom the native patella is left, the rate of reoperation is approximately 10%. However, when correct surgical technique is used, the rate of patellar complications after routine resurfacing is negligible. Although design modifications have helped reduce patellar complications, the surgeon is the most important variable. As long as good technique is used, routine patellar resurfacing has been proven to produce the best results in TKA.

Patellar position after total knee arthroplasty: influence of femoral component malposition

Patellar shift, tilt, and rotation were analyzed in 7 cadaveric knee specimens during simulated quadriceps loading, in the intact knee, and after implant reconstruction. Femoral component medialization, lateralization, and external rotation were also investigated. Relative motion of the patella with respect to the femur was measured using an electromagnetic tracking system. The spatial position of the patella did not change with standardized total knee arthroplasty (P <.05). After malpositioning of the femoral component, patellar rotation also did not change (P >.05); however, patellar tilt was altered by femoral component external rotation malposition (P <.05), and patellar shift was affected by all femoral component malpositions (P <.05). The spatial position of the patella relative to the femoral shaft was changed with any femoral component malposition, suggesting that the soft tissues were abnormally tensioned. This could result in subsequent wear on the patellar component and, therefore, early failure.

The trochlea is bilinear and oriented medially

Malfunctioning of total knee replacements often is related to patellofemoral problems. Because the trochlea guides the patella during flexion and extension, its geometry has a major influence in patellofemoral problems. There is controversy in the literature: relative to the mechanical axis, some authors have found a laterally oriented trochlea and others have found a medially oriented trochlea. The groove of implanted prosthetic femoral components always has lateral or neutral orientations. The objectives of the current study were to clarify the controversy found in the literature, to determine whether the trochlear orientation is truly linear, and to determine whether the orientation depends on the size of the femur. The trochleae of 100 human femurs were measured using a three-dimensional measurement system. Detailed analysis of the results indicated that the trochlea is best described as bilinear, with the distal half oriented 0.2 degrees +/- 2.8 degrees laterally and the proximal half oriented 4.2 degrees +/- 3.2 degrees medially. Trochlear orientation was not dependent on bone size.

Five year results of selective patellar resurfacing in cruciate sparing total knee replacements

We performed a prospective study on 129 knees with a selective approach to patellar resurfacing. One hundred and five knees were followed up at an average of 57 months. Of these, 48 knees met the eligibility criteria, thus leaving 57 knees with unresurfaced patellas. Mean follow up was 57 months. Parameters studied included HSS scores, pain, function, range of motion and patellofemoral symptoms including the ability to rise from a chair and to negotiate stairs. Approximately 90% good to excellent results were observed in both groups. The incidence of anterior knee pain and patellofemoral related problems was lower than the average reported in literature. None of the knees was revised for patellofemoral problems. Our findings suggest that the results of patellofemoral resurfacing with modern TKR designs are dependent on a careful patient selection and meticulous surgical technique. With a selective approach to resurfacing, one can achieve a high percentage of good results in both groups. Post-operative anterior knee pain is probably not related to the fact as to whether the patella is resurfaced or not.

Effect of femoral component design on unresurfaced patellas in knee arthroplasty

Three total knee designs were evaluated to test the hypothesis that femoral component design affects the clinical and mechanical functions of the unresurfaced patella after total knee arthroplasty. Patients with the Ortholoc II, Advantim, and Profix femoral components were followed up for as many as 14 years and revision rate, anterior knee pain, and generalized knee pain were compared. A laboratory protocol was devised to evaluate pressure in the patellofemoral joint of knees from cadavers with a pressure-sensitive transducer using the same three designs at various degrees of knee flexion. Thirty Ortholoc II knee components were followed up for 14 years. Nineteen patients (63%) had severe anterior knee pain and 15 patients (50%) had reoperation to resurface the patella within 2 years. Two hundred one patients (222 knees) with Advantim components were followed up for 10 years and 305 patients (330 knees) with Profix components were followed up for 5 years. No patients with these two knee designs had severe anterior knee pain or reoperation for patellar resurfacing. A significantly higher rate of mild anterior knee pain was seen in the patients with Advantim components than in the patients with Profix components. No apparent relationship was seen between the severity of patellar wear found at the time of surgery and the incidence of anterior knee pain. Patients with rheumatoid arthritis receiving either the Advantim or Profix knee component performed as well as patients with osteoarthritis when the patella was not resurfaced. Pressure was significantly higher in the patellofemoral joints of the laboratory knee specimens with Ortholoc II components than in the specimens with either the Advantim or Profix components. The specimens with Advantim components had significantly higher pressure than did the specimens with normal knees, and the specimens with Profix components differed little from those with normal knees.

Orthopaedic crossfire--All patellae should be resurfaced during primary total knee arthroplasty: in the affirmative

Patients with inflammatory arthritis, crystalline deposition disease, or severe patellofemoral arthritis have superior functional results with patellar resurfacing as compared with patellar retention. The only remaining issue is whether there is any advantage to resurfacing or retention in patients with osteoarthritic knees in the absence of severe patellofemoral arthritis. Although the answer is still unclear from available prospective randomized clinical trials, the evidence leans toward routine resurfacing of the patella during primary total knee arthroplasty in osteoarthritic knees too. Evidence exists that the results of patellar retention in osteoarthritic knees deteriorate with longer follow-up study. Long-term follow-up evaluations of available prospective clinical trials will be needed to assess this controversy more definitively.

Symmetrical vs asymmetrical total knee replacement--a medium term comparative analysis

Modifications of established implants can result in deleterious effects, as with the Capitol and the matt coated Exeter hips. In 1991 the Kinemax plus modification of the Kinematic knee was introduced in Bristol, the design changes having been made to reduce patello-femoral complications. We carried out a comparative analysis of the prospective recorded data on a consecutive series of 182 total knee replacements (95 Kinematic and 87 Kinemax plus knees) performed between 1991 and 1993. The same instrumentation and surgical technique was used. Since the design had introduced a broader trochlear, offset patella and had changed from an asymmetrical to a symmetrical femoral component, particular attention was paid to tracking and range of movement. All patients were reviewed at 5 years using the Bristol knee score and radiographs. There was no difference in the overall score (both prosthesis scoring 85-86) but the Kinemax plus group with a symmetrical trochlear had a significantly greater improvement in the range of movement (14 degrees as opposed to 4 degrees; P<0.05). In addition, secondary intervention for mal-tracking was significantly less in the Kinemax group. No deleterious effect of the changed geometry was observed. It is concluded that the introduction of a symmetrical femoral component with an offset patella reduced patello-femoral complications without detectable disadvantages.

Patellar resurfacing in total knee arthroplasty. A prospective, randomized study

BACKGROUND

Anterior knee pain following total knee arthroplasty is a common complaint and typically is attributed to the patellofemoral joint. The purpose of the present study was to compare the outcome of resurfacing and nonresurfacing of the patella, particularly with regard to anterior knee pain, and to clarify the indications for patellar resurfacing at the time of total knee arthroplasty.

METHODS

We performed a prospective, randomized study of 514 consecutive primary press-fit condylar total knee replacements. The patients were randomized to either resurfacing or retention of the patella. They were also randomized to either a cruciate-substituting or a cruciate-retaining prosthesis as part of a separate trial. The mean duration of follow-up was 5.3 years (range, two to 8.5 years), and the patients were assessed with use of the Knee Society rating, a clinical anterior knee pain score, and the British Orthopaedic Association patient-satisfaction score. The assessment was performed without the examiner knowing whether the patella had been resurfaced. At the time of follow-up, there were 474 knees. Thirty-five patients who had a bilateral knee replacement underwent resurfacing on one side only.

RESULTS

The overall prevalence of anterior knee pain was 25.1% (fifty-eight of 231 knees) in the nonresurfacing group, compared with 5.3% (thirteen of 243 knees) in the resurfacing group (p < 0.0001). There was one case of component loosening. Ten of eleven patients who underwent secondary resurfacing had complete relief of anterior knee pain. The overall postoperative knee scores were lower in the nonresurfacing group, and the difference was significant among patients with osteoarthritis (p < 0.01). There was no significant difference between the resurfacing and nonresurfacing groups with regard to the postoperative function score. Patients who had a bilateral knee replacement were more likely to prefer the resurfaced side.

CONCLUSIONS

As the present study showed a significantly higher rate of anterior knee pain following arthroplasty without patellar resurfacing, we recommend patellar resurfacing at the time of total knee replacement when technically possible.

Fate of the unrevised all-polyethylene patellar component in revision total knee arthroplasty

BACKGROUND

During revision total knee arthroplasty, the alternatives for addressing the well-positioned and secure all-polyethylene patellar component with minimal or no wear include retention, revision, and resection. The purpose of the present study was to determine the intermediate-term fate of all-polyethylene patellar components that were left in situ at the time of revision tibiofemoral arthroplasty.

METHODS

We retrospectively reviewed the results of 202 revision total knee arthroplasties, performed at four centers, in which a well-fixed, well-positioned all-polyethylene patellar component with minimal wear was retained. Clinical evaluation was performed to identify the presence of anterior knee symptoms or patellar failures, and the Knee Society clinical scores were recorded.

RESULTS

Sixty-eight percent of the revision tibiofemoral components were from a different manufacturer than the retained patellar component. Twenty-one patients (twenty-one knees; 10%) reported anterior knee pain at a mean duration of follow-up of seven years (range, two to fourteen years). Eleven of the twenty-one knees with anterior knee pain had evidence of component loosening, excessive wear, or delamination either on follow-up radiographs or on direct inspection at the time of reoperation. In the other ten knees, the findings were attributable to osseous impingement on the femoral component or soft-tissue dysfunction (including soft-tissue impingement, subluxation, and scarring). Seventeen of the twenty-one patients with anterior knee pain underwent additional surgery to address the source of the pain. Failures due to loosening or wear occurred only in patients in whom the patellar component had been sterilized with gamma irradiation in air; these failures occurred at a mean 7.3 years after revision (eleven years after primary total knee arthroplasty). The likelihood of patellar component failure was significantly greater when the component had been gamma irradiated in air than when it had been sterilized with another method (p = 0.0008). The average knee score increased from 42 to 86 points, and the average function score increased from 46 to 70 points.

CONCLUSIONS

Retaining a well-positioned, stable all-polyethylene patellar component at the time of revision tibiofemoral arthroplasty can be successful, provided that the polyethylene has not oxidized. Manufacturing mismatch is acceptable with most contemporary designs provided that the patellar component articulates appropriately with the femoral implant.

LEVEL OF EVIDENCE

Therapeutic study, Level IV (case series [no, or historical, control group]). See p. 2 for complete description of levels of evidence.

Long-term clinical results and radiographic changes in the nonresurfaced patella after total knee arthroplasty: 78 knees followed for mean 12 years

We evaluated total knee arthroplasty without patellar resurfacing retrospectively in 50 patients (78 knees; 4 men (7 knees) and 46 women (71 knees) having a mean age of 63 (34-78) years and mean weight of 52 (32-72) kg). The preoperative diagnosis was osteoarthrosis in 26 patients (43 knees) and rheumatoid arthritis in 24 (35 knees). The mean follow-up was 12 (9-14) years. Only 3 patients (4 knees) had patellar pain and they all showed patellar subluxation. The latter was found in 13 other knees, all pain-free. We detected no differences between the knees with osteoarthrosis and rheumatoid arthritis concerning the incidence of patellar pain and patellar subluxation. No patient needed revision surgery for patellar problems. We question the need to resurface the patella routinely in total knee arthroplasty if it is congruous and well-aligned.

Press-fit metal-backed rotating patella: seven- to 14-year followup

A consecutive series of 80 patients with 110 press-fit metal-backed rotating platform patella resurfacing surgeries were reviewed at an average of 107 months followup (range, 84-167 months). Twenty-eight patients died before followup. Fifty-two patients (70 patellae) were available for clinical and radiographic followups. One patella was revised for failure of the patella component. Four patellae were revised along with revision of the knee replacement. One patella realignment procedure was done for recurrent subluxation of the patella. There were no patellar dislocations in this series, no patella fractures, and no disruption of the quadriceps tendon or infrapatellar ligament. Six patellae had subluxation seen on postoperative radiographs. The incidence of patellar tilt greater than 5 degrees was 13%. No patellae were considered radiographically loose. The incidence of radiolucencies was 37%. Subsidence of the component superiorly was identified in 39% of the patellae, and inferiorly in 36% of the patellae. Of the 49 patients (67 knees) returning for followup, 70% of the knees were rated as excellent, 10% were rated good, 15% were rated fair, and 5% were rated poor. Press-fit metal-backed patella provided good component durability with only one revision because of component failure. Radiographic analyses showed a high incidence of subsidence associated with good clinical results.

Muscle torques in total knee arthroplasty with subvastus and parapatellar approaches

The current study was designed to compare muscle torques when using the subvastus and parapatellar approaches for unilateral total knee arthroplasty. Twelve female patients had unilateral total knee arthroplasty with the subvastus approach from January 1997 to June 1998. The historic control group consisted of 16 female patients who had unilateral total knee arthroplasty with the parapatellar approach from July 1994 to January 1997. Six and 12 months after surgery, a Cybex dynamometer was used to measure isometric and isokinetic muscle strength. Two parameters were used to compare the two approaches, the first parameter was the difference in peak torque between the surgically treated knee and the baseline value for the healthy knee, and the second parameter was the hamstring to quadriceps peak-torque ratio, again using the value for the healthy knee as baseline. The subvastus approach resulted in an initial higher peak torque in the quadriceps 6 months after surgery, but this difference became insignificant 12 months postoperative. Using the subvastus approach, the hamstring to quadriceps peak-torque ratio reached the normal range (0.50-0.80) sooner than was the case using the parapatellar approach. There is a phenomenon of cross adaptation of the untreated knee to the surgically treated knee, and knees operated on by the subvastus approach showed functional recovery at an earlier date than those operated on by the parapatellar approach.

Patellar component resection arthroplasty for the severely compromised patella

When severe bone loss precludes reimplantation of a new patellar component during revision knee arthroplasty, the treatment options include patellar bone grafting, patellar component resection arthroplasty, and patellectomy. The purpose of this study was to evaluate the clinical and functional results of patellar component resection arthroplasty for the severely compromised patella for which insertion of another patellar component was not possible. Thirty-five knees (31 patients) were treated with patellar component resection arthroplasty for aseptic patellar component failure associated with severely compromised patellar bone stock. Followup averaged 7.9 years (range, 2-18 years). There was a significant improvement in Knee Society pain and function scores. Pain relief was more dramatic than functional improvement. The range of motion also improved significantly and in particular preoperative extensor lag was resolved in the majority of patients. Patients treated with isolated patellar resection arthroplasty were more likely to have continuing pain and require reoperation compared with patients who had concomitant revision of the tibial and femoral components. Correct positioning and the stability of tibial and femoral components should be tested carefully at the time of patellar resection arthroplasty and considered for revision if malpositioned either axially or rotationally.

The Knee Society Index of Severity for failed total knee arthroplasty: development and validation

Compared with primary knee replacement, total knee arthroplasty revision surgery is a more complex procedure and accounts for greater expenditures of healthcare resources at each clinical stage. Overall, patients having revision procedures have poorer functional outcomes and higher complication rates than patients having primary arthroplasty. Despite the expanded scope of revision problems and the rapidly emerging technology in revision surgery, the long-term success of any method remains in question. Because there is little consensus on the timing of revision surgery, optimal surgical reconstruction, and the type of prosthesis to be implanted, the Knee Society began development of an Index of Severity for Failed Total Knee Arthroplasty. Fifty-four percent of Knee Society members completed an 82-item questionnaire that determined their clinical impression about potential risk factors for the outcomes of revision surgery for failed total knee replacements. Using these results, a consensus group developed the final version of the index. The result of the nominal group process was the Knee Society Index of Severity, which was based on eight distinct domains. Each domain was divided into attributes and weights based on the questionnaire responses and consensus meeting. Actual case scenarios from five institutions were used to test interrater reliability and validity. The interrater reliability of the average score of all ratings was 0.95; the correlation of the criterion rating with the mean rating was 0.77. When three outliers were not included, the Pearson product correlation increased to 0.92. These data support the application of the Knee Society Index of Severity as a critical component of risk factor studies, effectiveness research, and cost-effectiveness analysis involving revisions of total knee replacements.

Kinematics of the patellofemoral joint in total knee arthroplasty

Sagittal plane patellofemoral kinematics was determined for 81 subjects while performing a weight-bearing deep knee bend under fluoroscopic surveillance. Fourteen normal knees, 12 anterior cruciate ligament (ACL)-deficient knees, and 55 total knee arthroplasties (TKAs) were assessed. Of TKAs, 39 had resurfacing with a dome-shaped patella, 8 had resurfacing with an anatomic mobile-bearing patella, and 8 were unresurfaced. TKA patellae experienced more superior patellofemoral contact and higher patellar tilt angles compared with the normal knees and ACL-deficient knees (P <.05). Patellofemoral separation at 5 degrees (+/-3 degrees ) extension was seen in 86% cruciate-retaining and 44% cruciate-stabilized TKAs and 8% ACL-deficient knees but not in the normal knees or mobile-bearing TKAs (P <.05). The patellar kinematic patterns for subjects having a TKA were more variable than subjects having either a normal knee or an ACL-deficient knee. Kinematic abnormalities of the prosthetic patellofemoral joint may reduce the effective extensor moment after TKA.

Patella in total knee arthroplasty

The patella is a reliable guide to the success or failure of a total knee replacement. Patients who do not experience peripatellar symptoms or a patellar complication usually have a successful result. Conversely, peripatellar symptoms or complications usually reflect an underlying problem with surgical technique, component designs, or both. Current designs still do not replicate normal kinematics, and current instrumentation and techniques significantly alter the anatomy of the patellofemoral articulation in a substantial percentage of patients. Reproducing extensor mechanism balance and using components that provide adequate congruency and contact area through a physiologic arc of motion should lead to a successful result with minimal patellar symptoms or complications whether or not the patella is resurfaced. Attempting to achieve normal patellofemoral kinematics and minimize patellar complications has led to a better understanding of total knee arthroplasty.

The failure of all-polyethylene patellar components in total knee replacement

The patellar component of total knee replacement is the most frequent source of nonseptic complications after total knee arthroplasty. The purpose of the current study was to review the radiographic factors associated with loosening of all-polyethylene patellar components. Four thousand five hundred eighty-three cases of Anatomic Graduated Components total knee replacements were performed at the authors' institution during the past 15 years. Radiographs were reviewed and loosening was defined as global radiolucency or component migration. Four thousand two hundred eighty-seven allpolyethylene patellar components were implanted. There were 180 (4.2%) loose all-polyethylene patellar components. The mean time to loosening was 2.6 years (+/- 1.75 years). Fifteen (0.3%) patellar components required revision. Five radiographic features were associated with failure. The incidence and mean time of appearance were recorded: (number; incidence; time) (1) Bone-cement radiolucency, n = 174, 96.7%, 1.4 years; (2) increased density, n = 118, 65.6%, 1.8 years; (3) trabecular collapse of the bone, n = 160, 88.9%, 2.3 years; (4) patella fracture and fragmentation, n = 133, 73.9%, 2.5 years; and (5) lateral subluxation of the residual patella bone, n = 146, 81.1%, 2.9 years. Lateral retinacular release was associated with an increased rate of patellar loosening. Loosening of the allpolyethylene patella component is an avascular process strongly associated with lateral retinacular release and for which the patient infrequently requires revision surgery.

Total knee arthroplasty using cruciate-retaining kinematic condylar prosthesis

The purpose of the current study was to evaluate the long-term results of the Kinematic I condylar prosthesis with retention of the posterior cruciate ligament. One hundred sixty-eight total knee arthroplasties in 118 patients (mean age, 65.2 years; range, 21-88 years) were inserted with cement, an all-polyethylene patella, metal-backed tibia, and posterior cruciate ligament retention. Sixty-one patients (86 knees) died, one patient had an above-knee amputation, and three patients (five knees) were lost to followup; therefore, 66 knees (excluding revisions) in 50 patients were available for followup at a mean of 15.7 +/- 1.1 years (range, 14-20 years). Of the entire cohort of 168 knees, 13 have been revised: one for medial femoral condyle fracture, one for tibiofemoral instability, one for femoral and two for tibial component aseptic loosening, four for tibial polyethylene wear, and four for patellar component aseptic loosening. The 15-year survivorship free of any component revision excluding infections was 88.7% (confidence interval, 82%-95%). The 15-year survivorship free of radiographic loosening and/or revision of any component was 85.1% (confidence interval, 78%-92%). The current study shows good function and survivorship of the posterior cruciate-sparing Kinematic I condylar prosthesis at a mean of 15.7 +/- 1.1 years.

Should the patella be resurfaced at total knee replacement?

Total knee replacement (TKR) presumably is replacement of the total knee articular surface. Sometimes it is and sometimes it is not. It is this author's firm conviction that the patella should be resurfaced in the vast majority of cases. Such advocacy must be critically justified and the potential drawbacks and alternatives examined.

The effect of patella preparation for total knee arthroplasty on patellar strain: a comparison of resurfacing versus inset implants

This study was conceived to quantify variables in surgical technique that may lead to patellar fracture after total knee arthroplasty. Anterior surface strain on load-bearing cadaveric patellae was measured before and after patellar resurfacing or inset prosthesis placement. Variables studied were i) the type of prosthesis (resurfacing vs inset), ii) the depth of reaming or osteotomy during surface preparation, and iii) the overall thickness of the polyethylene/patella composite after implantation. Comparison of measured patellar surface strain patterns for the different prosthesis styles, which were implanted at varying depths, provided statistically significant data from which the following clinically relevant conclusions can be made: i) Patellar resurfacing is superior to inset prosthesis placement when comparing postoperative patellar strain (22% vs 28% increase in strain compared with preoperative values). ii) Osteotomy for patellar resurfacing is more tolerant to error by excess cutting than is reaming for inset prosthesis placement (25% vs 42% increase in strain with a 2-mm error). iii) If the ideal depth of cut or reaming is surpassed, attempts to re-create the original patellar thickness by using a thicker prosthesis are mechanically detrimental. Key words: patella, strain, resurfacing, complications.

Computer-assisted decision analysis in orthopedics: resurfacing the patella in total knee arthroplasty as an example

The purpose of the present study was to illustrate the use of computer-assisted decision analysis in making decisions in the field of orthopaedic surgery, using the choice between resurfacing and not resurfacing the patella in total knee arthroplasty as an example. We used a decision analysis technique based on probability theory and on Bayesian logic, with the help of an especially developed computer software. The process involves building a decision tree, searching for probabilities and utilities in the literature, folding back the tree to compute the baseline result, and running sensitivity analyses. Our literature search provided 26 useful articles, only 3 of which were randomized controlled trials. In the baseline analysis, both options were rated similarly, with resurfacing the patella faring slightly better. Sensitivity analyses revealed that not resurfacing becomes the procedure of choice if the probability of postoperative anterior knee pain with an unresurfaced patella falls below 14%, or if the probability of having pain with a resurfaced patella rises above 8% or if the utility of patellar implant failure falls below 80% of the utility of a perfect health state. Computer-assisted decision analysis is a promising, evidence-based tool to assist clinical decision making in orthopaedic surgery. However, its validity is limited by the poor quality of data found in the orthopaedic literature, especially the scarcity of randomized controlled trials.

Patellar resurfacing in total knee arthroplasty

Whether or not to resurface the patella when performing a primary total knee arthroplasty remains an open question. A number of recent studies have added new information relevant to this controversy. Anatomic studies show that there is normally substantial variability in the anatomy of the trochlear groove. Implanting a femoral component therefore results in a change in the surface topography of the knee in a high percentage of cases. Even though a number of intraoperative techniques have been described in an attempt to accurately reproduce femoral and tibial component rotation, studies of the application of these techniques reveal that component malpositioning or malrotation of a measurable degree occurs in 10% to 30% of cases, depending on the surgical technique and landmarks used. There has been substantial change in the design of both femoral and patellar components in recent years. Even with current designs, biomechanical studies indicate that some degree of change in kinematics and contact stresses occurs following total knee arthroplasty. However, the results of clinical studies have been extremely variable, with most showing either no difference or very little difference between resurfaced and nonresurfaced patellae in osteoarthritic knees. The decision to resurface the patella or not must be individualized on the basis of the surgeon's training and experience and an intraoperative assessment of the patellofemoral articulation.

Contact stresses with an unresurfaced patella in total knee arthroplasty: the effect of femoral component design

Compressive contact stresses between the patella and the anterior femur were measured with a digital electronic sensor before and after total knee arthroplasty (TKA) in 10 cadaver knee specimens. Contact stresses were measured first in normal knees, then after TKA with the Insall-Burstein Total Condylar, Miller Galante II, Ortholoc II, Porous Coated Anatomic, and Profix knee prostheses implanted without resurfacing the patella. The Insall-Burstein, Miller-Galante II, and Ortholoc II prostheses had significantly higher contact stresses than the normal knee throughout the flexion arc. The Porous Coated Anatomic, which has a smooth patellar groove, maintained contact area as in the normal knee and did not have significantly higher contact stresses at flexion angles <90 degrees. At flexion angles > or =105 degrees, patellofemoral contact occurred in two small areas as the patella encountered the intercondylar notch in all components except the Profix. The Profix maintained full contact and low compressive stresses throughout the full flexion arc because of its posteriorly extended patellar groove. Design features of the patellofemoral portion of TKA components are important factors that affect contact stresses in the patellofemoral joint. These features likely will affect the clinical results of TKA with an unresurfaced patella.

Patellar component positioning in total knee arthroplasty

Five human anatomic specimen knees were used to determine the effect of patellar component position on patellofemoral kinematics, contact pressures, and contact areas after total knee arthroplasty using a polyethylene, domed patellar component. Each patellar component was positioned at the anatomic center of the resected patellar surface and then repositioned 5 mm proximally, distally, medially, and laterally. Patellar tilt was greatest with medial positioning of the patellar component and least with central and lateral positioning. At higher knee flexion angles, patellofemoral joint contact pressures increased at the medial facet with the medialized component and at the lateral facet for the lateralized component. The centralized component had the most evenly balanced patellar facet contact pressures. Distally positioned patellar components resulted in decreased patellar component loading at higher knee flexion angles. Central positioning of the patellar component results in optimal patellofemoral mechanics when maximal coverage of the resected patella is desired.

Patellar contact forces with and without patellar resurfacing in total knee arthroplasty

Patellar contact forces were measured in 7 fresh-frozen cadaver knees during continuous flexion-extension cycling for the normal knee and after total knee arthroplasty without and with patellar resurfacing using 2 prosthesis systems with different designs for the femoral and patellar components. Analysis of variance with specimen as a repeated measure was used to examine the effect of contact surface. When compared to normal knees, total knee arthroplasty without patellar resurfacing resulted in no change in patellar contact forces. The magnitude of the inferosuperior patellar shear force increased significantly after patellar replacement with an oval, biconcave patellar component and increased further after replacement with an oval, domed patellar component. There were no significant changes in the mediolateral and anteroposterior contact force components after patellar replacement.

Kinematic total knee arthroplasty: a 10- to 14-year prospective follow-up review

To understand better the type and incidence of long-term complications in total knee replacement, 306 primary Kinematic total knee arthroplasties performed between June 1978 and December 1982 were prospectively reviewed in detail. The Kinematic knee is a nonconstrained, posterior cruciate-retaining prosthesis that has right and left femoral components to afford anatomic tracking of the patella. The overall revision rate was 6.5%. The most common cause for revision surgery was patellar complications. Ten revisions (3.06%) were for patellar component loosening. Two knees were revised for patella subluxation (0.65%); 1 was in a resurfaced rheumatoid patella, and 1 in an unsurfaced osteoarthritic patella. Stair climbing was better with an unsurfaced patella. Anterior knee pain was 21.8% in the unsurfaced patella and 11.2% in the replaced patella. These data suggest patella replacement is not appropriate with this design.

Edge loading of patellar components after total knee arthroplasty

Patellofemoral joint kinematics, contact areas, contact pressures, and contact patterns were assessed after total knee arthroplasty (TKA) using human cadaver knees. Two contemporary TKA systems with anatomic patellofemoral joints were implanted and tested under anatomically based loading conditions. An electromagnetic tracking system was used to evaluate patellofemoral kinematics, and Fuji pressure-sensitive film was used to determine contact areas, pressures, and patterns. Edge loading of patellar components was observed at higher knee flexion angles with both TKA systems. Peak contact pressures seen at the regions of edge loading exceeded the yield strength of ultra-high-molecular weight polyethylene. Efforts to reduce edge loading and contact pressures may decrease the incidence of patellofemoral joint complications and component failure after TKA.