Soft tissue balancing of the “flexion gap” has a direct affect on patello-femoral tracking. Both of which are necessary for a well functioning Total Knee Arthroplasty (TKA). Traditionally, successful restoration of soft tissue balance and patellar tracking depend heavily on surgeon experience, empirical judgment and technical skill.

Orthopaedic residents often are confronted with the challenge of learning to perform TKA without objective measures with which to assess the accuracy of their surgical technique. Also, the vast majority of TKA’s are performed by surgeons who do less than 25 TKA’s per year. Both populations often rely upon surgical release of the lateral patellar retinacular tissues in order to restore “optimal” patellar tracking. This surgical technique is often associated with division of the lateral geniculate vessels and increased potential for avascular necrosis of the patella and lateral subcutaneous hematoma. Both groups of surgeons would be well served if there were available a means with which they could objectively measure whether or not they have in fact achieved the soft tissue balance they intended and optimal patello-femoral tracking, without the need for a lateral release.

Historically, the incidence of lateral release, as a means of improving patellofemoral tracking, has been reported performed in more than 10% of TKA. A prospective group of 200 consecutive TKA’s, performed by two surgeons, in which an electronic means of assessing “flexion gap” balance was retrospectively reviewed for the incidence of intra-operative lateral release. It was found that use of electronic measurement to assure “flexion gap” balance was associated with a significant reduction in the incidence of lateral release required to achieve optimal patello-femoral tracking.

Introduction: Cemented stems are still widely used in THA; however, there remain concerns with hip dislocation and wear debris. Restoring joint mechanics is essential for soft tissue balance and reduction of mechanical impingement. These concerns have lead to the development of a modular neck for cemented THA.

Material and methods: 200 R-120™ cemented stems were implanted in 190 patients since 2001. The shape of the stem is trapezoidal with a large collar that provides for impaction and compression of the cement. The stem collar is made with a cavity where a self-locking taper and a positive indexing mechanism provide 12 different positions to ensure proper restoration of joint mechanics.

One to five years follow up with a mean of 2.8 years. Two-thirds were female and one- third male. Age ranged from 39 to 87 with a mean of 73. Majority was treated for OA. A c.c. head (28mm or 32mm) and poly bearing in a cementless cup were used for all patients. Selection of neck position was recorded for all patients.

Results: 635 of all head-neck positions were other than neutral. There were 0 dislocations, no significant leg length discrepancies (+/− 5mm), and 0 infections. There was one stem removed due to a post-op peri-prosthetic fracture at 3 years that was treated with a long cement-less stem. 1 death due to a PE ten days post-op. 1 intra-operative calcar fracture wired and healed uneventfully. 1 intra-op greater trochanter fracture that was treated with screws. 2 neck fractures revised to cementless stems.

Conclusions: Modular neck design aids in fine tuning joint mechanics after stem insertion, and allows for ease and access in case of revisions. This modular neck design has eliminated (to date) hip dislocations and we remain optimistic about its long-term potential to improve outcomes. Fatigue properties have been significantly improved and no additional neck fractures have occurred.

There is interest to provide total knee arthroplasty (TKA) patients large ranges of functional knee flexion. Factors contributing to flexion include a posterior femoral position on the tibia, posterior condylar offset, and posterior tibial slope. These factors can be incorporated into implant designs and surgical techniques. It is useful to assess the robustness of the resulting design, that is, the consistency of kinematic or functional results when patient and surgical factors vary widely. This study evaluates in vivo flexion performance of a single implant design in patients whose posterior cruciate ligament (PCL) was either retained or sacrificed.

28 knees in 20 patients were imaged using fluoroscopy during maximum flexion kneeling and lunge activities. 20 knees (12 patients) received TKA with the PCL retained by a bone block (PCL+ group). Eight knees (7 patients) received TKA with complete PCL resection (PCL- group). All knees received a fixed-bearing TKA (3D Knee^™, Encore Medical, Austin, TX) with an asymmetric tibial bearing having a sagittally curved medial compartment and a lateral compartment fully congruous with the lateral condyle in extension (approximating anterior cruciate ligament substitution). Three-dimensional knee kinematics were determined using model-based shape registration techniques.

For the kneeling activity, mean implant flexion was 124°±11° for PCL+ knees and 121°±17° for PCL- knees (p> 0.05), mean tibial internal rotation was 10°±4° for PCL+ knees and 9°±3° for PCL- knees (p> 0.05) and tibial valgus was −1°±1° for PCL+ knees and 2°±4° for PCL- knees (p=0.003). Medial contact location averaged −2±4mm and for PCL+ knees and −1±2mm for PCL- knees (p> 0.05). Lateral contact location averaged −10±4mm for PCL+ knees and −7±1mm for PCL- knees (p> 0.05). For the lunge activity, mean implant flexion was 120°±11° for PCL+ knees and 121°±21° for PCL- knees (p> 0.05), mean tibial internal rotation was 11°±4° for PCL+ knees and 8°±3° for PCL- knees (p> 0.05) and tibial valgus was −1°±1° for PCL+ knees and 2°±2° for PCL- knees (p=0.0002). Medial contact location averaged 0±4mm for PCL+ knees and −4±3mm for PCL- knees (p=0.04). Lateral contact location averaged −8±4mm for PCL+ knees and −9±4mm for PCL- knees (p> 0.05).

There was no difference in implant flexion between PCL retaining and sacrificing TKA. Both groups had knees with more than 145° implant flexion (~155° skeletal flexion). There were no significant differences in tibial rotation or lateral condylar contact locations. There were differences in tibial valgus for both activities. PCL- knees exhibited a tendency for the medial compartment to ‘book open’ with flexion beyond 130°, consistent with loss of PCL function. Based on this small cohort comparison, it appears that robust flexion performance and knee kinematics can be obtained with a fixed-bearing TKA design.