Tibiofemoral contact stress after total knee arthroplasty

We measured tibiofemoral contact stresses and the load-bearing contact area of fixed and mobile-bearing inlay knee prostheses under dynamic loading conditions. An electronic resistive pressure-measuring sensor was used to detect contact stresses and contact area in five cadaver knees. Stresses were measured with the tibial component aligned normally, as well as in internally- and externally-rotated positions. The average peak contact stresses measured on the fixed inlay were greater (medial 21 MPa and lateral 21 MPa) than those on the mobile inlay (medial/lateral 7.7/5.3 MPa, p = 0.04). Although the average peak contact stresses of the fixed standard inlay greatly exceeded the contact stresses of the other two inlay designs in each malrotated position tested, no statistically significant differences were seen. The data suggest that the ability of the inlay to translate on the tibial baseplate permits the inlay to align itself on the femoral component so that the contact surface area is maximized and contact stresses are reduced.     

Patellofemoral function after total knee arthroplasty: gender-related differences

The purpose of the study was to evaluate patellofemoral results in 2 comparable groups of 50 patients, men and women, undergoing total knee arthroplasty. The average follow-up was 6 years. The implant was posteriorly stabilized with a dome patellar arthroplasty. The patients were studied using Knee Society knee and functional scores and the Hospital for Special Surgery (HSS) patellar score. Radiologic study included standard and weight-bearing axial views and a computed tomographic scan to assess component rotation. The 2 groups achieved satisfactory and similar knee scores; women had a significantly lower functional and patellar scores. The incidence of lateral patellar tilt, subluxation, and lateral impingement was decreased in weight-bearing axial views compared with non-weight bearing. Medial bony impingement was evident only in weight-bearing views and correlated with pain (P < .05).     

Patellofemoral joint contact area increases with knee flexion and weight-bearing.

Patellofemoral pain is a common and debilitating disorder. Elevated cartilage stress of the patellofemoral joint is hypothesized to play a role in the onset of pain. Estimating cartilage stress requires accurate measurements of contact area. The purpose of this study was to estimate patellofemoral joint contact areas in a group of healthy, pain-free subjects during upright, weight-bearing conditions. Sixteen subjects (8 female, 8 male) were scanned in a GE Signa SP open configuration MRI scanner, which allowed subjects to stand or squat while reclining 25 degrees from vertical with the knee positioned at 0 degrees , 30 degrees , or 60 degrees of flexion. A custom-built backrest enabled subjects to be scanned without motion artifact in both weight-bearing (0.45 body weight per leg) and reduced loading conditions ('unloaded' at 0.15 body weight) at each knee flexion posture. Male subjects displayed mean unloaded patellofemoral joint contact areas of 210, 414, and 520 mm(2) at 0 degrees , 30 degrees and 60 degrees of knee flexion, respectively. Female subjects' unloaded contact areas were similar at full extension (0 degrees ), but significantly smaller at 30 degrees and 60 degrees (p<0.01), with mean values of 269 and 396 mm(2), respectively. When normalized by patellar dimensions (heightxwidth), contact areas were not different between genders. Under weight-bearing conditions, contact areas increased by an average of 24% (p<0.05). This study highlights the differences in patellofemoral joint contact area between gender, knee flexion postures, and physiologic loading conditions.     

Patellofemoral resurfacing at total knee arthroplasty

A retrospective review of 268 primary total knee arthroplasties (TKAs) with a mean follow-up of four years is presented. The patellae were resurfaced in all cases. There were six complications (2.2%) referable to the patellofemoral articulation: three subluxations, one patellar fracture, one loosening of a metal-backed patellar component, and one patellar tendon avulsion. Successful patellofemoral resurfacing (PFR) can be accomplished with minimal complications if the following technical considerations are met: 5-7 degrees of valgus alignment; medial placement of the patellar component; taking care not to increase either the AP diameter of the knee or the thickness of the patella; avoiding internal rotation of either the tibial or femoral components and proper soft tissue balancing. A thorough review of patellofemoral complications after TKA is presented, and technical considerations relevant to the successful performance of PFR are discussed.     

Periprosthetic tibial fractures after cementless low contact stress total knee arthroplasty

Periprosthetic fractures are a recognized complication of total knee arthroplasty. Fractures may occur intraoperatively or postoperatively, and risk factors have been identified that may predispose an individual to such a complication. We report 7 cases of periprosthetic tibial fractures after low contact stress total knee arthroplasty, a complication encountered by the senior author (D.E.B.) only after a change in practice from a cemented implant to a cementless one. In light of this previously unreported complication in our unit, we attempted to identify common features within this group of patients that may have contributed to fracture occurrence. Statistical analysis revealed a highly significant (P<.005) risk of periprosthetic tibial fracture in patients with a preoperative neutral or valgus knee. Age, gender, and diagnosis did not appear to increase the risk of fracture significantly. All patients displayed evidence of reduced bone mineral density in the lumbar spine and femoral neck regions on dual-energy x-ray absorptiometry scanning. Patients with a preoperative neutral or valgus knee and local evidence of osteopenia represent a high-risk group, in whom particular care in alignment should be taken. In this group, it may be preferable to have the tibial component inserted with cement fixation.     

Effect of patellar meniscus on patellofemoral contact stress in total knee arthroplasty

The effect of a meniscus of fibrous tissue (patellar meniscus), on patellofemoral contact area and stresses was evaluated. Two knees with total knee arthroplasty and dome-shaped patellar components were retrieved at autopsy. Both had substantial fibrous menisci surrounding the dome of the patellar component. Contact area and contact stresses were measured with a digital electronic sensor, first with the patellar meniscus intact, then again after the patellar meniscus was removed. No dramatic difference was detected in patellofemoral contact area and contact stresses between the patellas with an intact or removed patellar meniscus, and there was no detectable load under the patellar meniscus. The results of this case study suggest that fibrous tissue surrounding the dome-shaped patellar component does not share compressive loads with the patellar component.     

Patellofemoral function in total condylar knee arthroplasty

Summary A series of 100 total condylar knee arthroplasties was studied to determine radiographic and clinical patellofemoral function. Before operation there was lateral patellar tilt in 31 cases and lateral displacement in 52. After operation tilt was present in 8 and displacement in 14. Only a few patients had medial patellar displacement. Dislocation or fracture of the patella was not encountered. Six patients had postoperative patellar pain. In one case there was a radiolucent zone at the bone-cement interface in the patella, without pain. Patellofemoral function before operation was good in 3, fair in 54, and poor in 43 cases. After operation it was good in 88 and fair in 12. Both tilt and displacement slightly reduced postoperative patellofemoral function. Patellar reconstruction with the total condylar prothesis shows reasonably good tolerance of moderate malpositioning of the patellar prosthesis, affords sufficient stability and usually painless patellofemoral function.

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Résumé Les auteurs ont étudié une série de 100 arthroplasties du genou de type »total condylar« afin d'apprécier cliniquement et radiologiquement la fonction fémoro-patellaire. Avant l'opération il existait une bascule externe de la rotule dans 31 cas et une subluxation externe dans 52. Après l'opération, la bascule a été retrouvée 8 fois et la subluxation 14 fois. Quelques malades seulement présentaient une subluxation interne. Il n'y avait ni luxation ni fracture de la rotule. Six opérés se plaignaient de douleurs rotuliennes. Dans un cas on notait sur la radiographie une zone claire entre l'os et le ciment, mais sans douleur. La fonction fémoro-patellaire avant l'opération était bonne dans 3 cas, passable dans 54 et mauvaise dans 43. Après l'opération, elle était bonne 88 fois et passable 12 fois. Aussi bien la bascule que la subluxation réduisent un peu la fonction post-opératoire de l'articulation fémoropatellaire. La reconstruction de la rotule lors de l'arthroplastie »total condylar« tolère une légère malposition de la prothèse rotulienne, assure une stabilité suffisante et, habituellement, une fonction indolore.

     

Patellofemoral complications in symmetrical total knee arthroplasty

A review of 356 Kinemax (Howmedica, Inc, Rutherford, NJ) cemented posterior cruciate ligament-retaining condylar total knee arthroplasties employing a symmetrical femoral component articulating with a medially offset symmetrical dome patella component was carried out to examine the results and determine the incidence and nature of the patellofemoral complications. Follow-up was from 3 to 8 years, with a mean of 5.1 years. A review of patellofemoral complications in previously reported homogeneous series of symmetrical and asymmetrical implants is presented. Mean postoperative Knee Society scores improved to 91, function scores to 86, and Hospital of Special Surgery scores to 90 yielding 95% good and excellent results. Mean postoperative range of motion was −1.5° extension to 113° flexion. There were five patellofemoral complications (1.4%), including two symptomatic subluxations, two distal pole avulsion fractures, and one lateral facet fracture. There were two reoperations necessary for patellofemoral problems (0.56%), one to correct subluxation and one for excision of the fractured lateral facet. These rates are lower than those previously reported for asymmetrical implants as well as current and phased-out symmetrical designs of total knee arthroplasty in the intermediate term. This review suggests that cemented total knee arthroplasty with symmetrical patellofemoral resurfacing with an offset patella dome and posterior cruciate ligament retention yields low patellofemoral complications and reoperations. The symmetrical femoral component appears to be a satisfactory compromise of “normal” femoral anatomy, which decreases inventory and cost without adversely affecting patellofemoral function and complications.     

Periprosthetic fractures after total knee joint arthroplasty

Periprosthetic fractures of the femur, tibia and patella are being registered with increasing frequency due to the rising numbers of total knee replacements. Depending on the site of the fracture, apart from mere traumatic mechanisms, implant specific parameters and implant loosening may represent the main causes of periprosthetic fracture. Moreover, general risk factors promote the manifestation of a periprosthetic fracture. Nowadays, valid classifications are available to categorize periprosthetic fractures of the femur, tibia and patella, and to create the basis for specific decision-making in choice of treatment. Despite a wide field of treatment options, the actual functional outcome after therapy and the high rates of complications imply that an adequate analysis of the fracture etiology and the corresponding transfer into an individualized treatment concept offer the chance of functional restoration of the patient similar to the pre-fracture state.     

Dislocation of the rotating platform after low contact stress total knee arthroplasty

From a one-surgeon series of 2485 patients, we report on 10 patients with rotating platform dislocation after primary Low Contact Stress total knee arthroplasty. All dislocations occurred within 2 years of the index procedure. Of the 10 patients, nine required open reduction. Five of these patients also had exchange of the original insert. One patient was treated by closed reduction. All knees were immobilized in a cast for 8 weeks. Eight of the 10 patients had no additional dislocation and at followup (average, 35 months; range, 12 months-5 years), had a stable functional joint. Two patients had recurrent spinout of the rotating platform develop. One patient had arthrodesis whereas the other patient had the insert cemented to the tibial tray as a salvage procedure. Increasing age, a preoperative valgus deformity, and prior patellectomy were significantly associated with rotating platform spinout. Surgical experience and an improved understanding of the soft tissue constraints, particularly in the valgus knee, are important in minimizing this complication.     

Position of the knee joint after total joint arthroplasty

A method for assessing knee joint position after surgery using the preoperative long-leg radiograph and the postoperative knee radiograph is described. Assessment of the formula has shown a near perfect correlation between the calculated position on the long-leg radiograph compared with the measured position for 44 knees. Three hundred eighteen knees after total joint arthroplasty were retrospectively reviewed and the postoperative position was determined. The preoperative position of the mechanical axis was 14.5 ± 37.3 mm medial to the knee joint center. Using the standing knee radiograph the postoperative position of the mechanical axis was 3.07 ± 9.2 mm lateral to the knee joint center, while the portable radiograph placed the mechanical axis 4.5 ± 12.4 mm medial to the knee joint center. There was a highly significant difference in the position of the knee joint center depending on the radiograph used for calculation (standing or portable). The difference between the two means was not due to opening of the knee joint, but likely due to change in the rotation of the knee in the presence of knee flexion. This series of the knee arthroplasties has a low projected rate of aseptic failure.     

Tibiofemoral contact stress after total knee arthroplasty: Comparison of fixed and mobile-bearing inlay designs

We measured tibiofemoral contact stresses and the load-bearing contact area of fixed and mobile-bearing inlay knee prostheses under dynamic loading conditions. An electronic resistive pressuremeasuring sensor was used to detect contact stresses and contact area in five cadaver knees. Stresses were measured with the tibial component aligned normally, as well as in internally- and externally-rotated positions. The average peak contact stresses measured on the fixed inlay were greater (medial 21 MPa and lateral 21 MPa) than those on the mobile inlay (medial/lateral 7.7/5.3 MPa, p = 0.04). Although the average peak contact stresses of the fixed standard inlay greatly exceeded the contact stresses of the other two inlay designs in each malrotated position tested, no statistically significant differences were seen. The data suggest that the ability of the inlay to translate on the tibial baseplate permits the inlay to align itself on the femoral component so that the contact surface area is maximized and contact stresses are reduced.     

Patellofemoral function after total knee arthroplasty: a comparison of 2 posterior-stabilized designs

Knee complications and function were analyzed in patients with 2 different posterior-stabilized total knee arthroplasty (TKA) designs, Optetrak 913 and Insall-Burstein II. Three hundred Insall-Burstein II knees with mean follow-up of 8 years (range: 5-9 years) and 300 Optetrak knees with mean follow-up of 6 years (range: 5-7 years) were studied. Lateral retinacular release was performed in 30% of Insall-Burstein II patients and 16% of Optetrak patients (P = 0.001), and patellar clunk was 4% for the Insall-Burstein II prosthesis and 0.3% for the Optetrak prosthesis (P = 0.003). No statistically significant differences in dislocation, fracture, or loosening rates were observed between the 2 groups. Knee Society scores were similar in 2 groups of 50 patients brought back to the office. Mean Knee Society knee scores were 92 and 94 for the Insall-Burstein II and Optetrak groups, respectively (P > 0.05), and function scores were 80 and 84 for the 2 groups, respectively (P > 0.05). At mid-term follow-up, Optetrak patients were less likely than Insall-Burstein II patients to require lateral retinacular release and experience patellar clunk.     

Patellofemoral pain after total knee arthroplasty: clinical pathway and review of the literature

Total knee arthroplasty (TKA) is an operation with a high gain in quality of life. However, some patients suffer from pain, limited range of motion, instability, infections or other postoperative complications. Patellofemoral pain (PFP) in particular is a common complication after TKA and is often responsible for revision surgery. In particular increasing and localized contact pressure and patella maltracking are held accountable for patellofemoral pain but the reasons are various. Diagnostics and therapy of patellofemoral pain is not easy to handle and should be treated following a clinical pathway. We suggest that patients with patellofemoral pain should be classified into four groups according to the suspected diagnosis after basic diagnostic measures as 1) tenidinosis, 2) mechanical reasons, 3) intraarticular non-mechanical reasons and 4) neurogenic psychogenic reasons. Efficient application of special diagnostic measures and further therapy is facilitated by this classification.     

Tibiofemoral contact stress after total knee arthroplasty: comparison of fixed and mobile-bearing inlay designs

We measured tibiofemoral contact stresses and the load-bearing contact area of fixed and mobile-bearing inlay knee prostheses under dynamic loading conditions. An electronic resistive pressure-measuring sensor was used to detect contact stresses and contact area in five cadaver knees. Stresses were measured with the tibial component aligned normally, as well as in internally- and externally-rotated positions. The average peak contact stresses measured on the fixed inlay were greater (medial 21 MPa and lateral 21 MPa) than those on the mobile inlay (medial/lateral 7.7/5.3 MPa, p = 0.04). Although the average peak contact stresses of the fixed standard inlay greatly exceeded the contact stresses of the other two inlay designs in each malrotated position tested, no statistically significant differences were seen. The data suggest that the ability of the inlay to translate on the tibial baseplate permits the inlay to align itself on the femoral component so that the contact surface area is maximized and contact stresses are reduced.     

Fungal prosthetic joint infection after total knee arthroplasty

Fungal prosthetic joint infection after total knee arthroplasty (TKA) is a rare complication. Lacunae exist in the management of this complication. 62 year old lady presented with pain and swelling in left knee and was diagnosed as Candida tropicalis fungal infection after TKA. She underwent debridement, resection arthroplasty and antifungal plus antibiotic loaded cement spacer insertion, antifungal therapy with fluconazole followed by delayed revision TKA and further fluconazole therapy. Total duration of fluconazole therapy was 30 weeks. At 2 year followup, she has pain less range of motion of 10^°-90^° and there is no evidence of recurrence of infection.     

减少髌骨厚度对膝关节置换术后髌股关节功能的影响

目的探讨减少髌骨厚度对膝关节置换术后髌股关节功能的影响。 方法收集2014年7月至2016年7月间在作者本院行单侧初次全膝关节置换术的122病例资料,分为常规髌骨打磨组与减少髌骨厚度组,术后随访2年。观察比较两组患者的一般情况、术前术后膝关节功能评分（HSS评分）、髌骨评分（Feller评分）、疼痛视觉模拟评分（VAS评分）,复查X线观察髌骨倾斜角、合适角。 结果术前两组一般资料无差异性,术前的HSS评分及Feller评分比较,差异无统计学意义。两组患者术后3个月、术后半年、术后1年及术后2年HSS评分、Feller评分、疼痛评分（VAS）及膝关节活动度经过重复测量设计的方差分析,显示两组的组间差异有统计学意义（P<0.05）,组别与时间点间存在交互作用,减少髌骨厚度组及常规髌骨打磨组在除术后1月外的其余术后各时间点间差异均有统计学意义。术后随访X线的髌骨倾斜角及合适角的对比无差异性。 结论全膝关节置换术可明显改善膝关节功能,如适当减少髌骨厚度,减轻髌股关节压力,较常规髌骨打磨更有利于改善髌股关节功能。但减少髌骨厚度的远期疗效及可能出现的并发症有待进一步随访、观察。     

Tibial stress fracture after computer-navigated total knee arthroplasty

A correct alignment of the tibial and femoral component is one of the most important factors determining favourable long-term results of a total knee arthroplasty (TKA). The accuracy provided by the use of the computer navigation systems has been widely described in the literature so that their use has become increasingly popular in recent years; however, unpredictable complications, such as displaced or stress femoral or tibial fractures, have been reported to occur a few weeks after the operation. We present a case of a stress tibial fracture that occurred after a TKA performed with the use of a computer navigation system. The stress fracture, which eventually healed without further complications, occurred at one of the pinhole sites used for the placement of the tibial trackers.