Rotational alignment of the tibial component in total knee arthroplasty.

This study compares two different methods of aligning the tibial component in a total knee arthroplasty, one by aligning the component with the border between the medial one third and lateral two thirds of the tibial tubercle and the other by allowing the component to seek its own position as the knee is taken through a range of motion. The first technique emphasizes the need to maintain an appropriate quadriceps angle for optimum patellar tracking and the second method optimizes femorotibial kinematics. The two methods suggest different positions for the tibial component, with the tibial component internally rotated an average of 5.6 mm from the border between the medial one third and lateral two thirds of the tibial tubercle when allowed to seek its own rotation. Surgeons must be aware of the choices they are making when selecting a method of aligning the tibial component. The prosthesis used in this study had a relatively high level of rotational constraint. The situation is somewhat different in a less constrained design.

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.

Patellar tilt and subluxation following subvastus and parapatellar approach in total knee arthroplasty. Implication for surgical technique.

Eighty-nine posterior-stabilized total knee arthroplasties (TKAs) were studied using a Merchant view to assess patellar tilt or subluxation. Forty TKAs were performed via the subvastus approach (SVA) and 49 via the standard parapatellar approach (PPA). Intraoperative tracking was assessed using a "no thumbs" test, and a lateral release was performed if necessary. Following the SVA, 40.0% of patellas tracked centrally compared to 44.9% for the PPA. With the SVA, a lateral release was necessary in 27.5% of procedures compared to 51.0% for the PPA. The data suggest that the no thumbs test may overestimate the need for lateral release following the PPA. Since there are fewer lateral releases following the SVA, reapproximation of the medial retinaculum to assess intraoperative tracking may result in fewer lateral release being performed without adversely affecting patellar position. Medial tilting of the patella is also found to be common; 29.7% of the patellas tilted this way, including 40.0% of knees operated via the SVA. Why this occurs is unclear, but the incidence of medial tilting increased after posterior-stabilized TKA.

Patellar tilt and subluxation in total knee arthroplasty. Relationship to pain, fixation, and design.

Two hundred thirty-four primary total knee prostheses were evaluated with a 45 degrees merchant view to examine patellar position and fixation. Despite a standardized technique for obtaining roentgenographs, patellar position varied with leg position. Overall, 54.7% tracked centrally, 31.2% tilted, and 14.5% displaced. The incidence of these findings was the same whether the patella was domed or congruent. Neither pain scores nor fixation were affected by position. Postoperative tilt and displacement were more common in patellae that were tilted preoperatively. The incidence of postoperative tilt or displacement was not significantly different in knees in which a lateral release was performed. Patellar tilt in some patients seems inevitable despite careful technique because intraoperative tests are static and postoperative function is dynamic. This does not bode well for wear in a metal-backed patella. Tilt caused increased loading at the periphery of the component where most metal-backed prostheses have thin polyethylene.

The brachial plexus. Clinical anatomy.

Brachial plexus injuries present in certain consistent patterns. Learning the overall brachial plexus anatomy--with an emphasis on the common sites of injury--can facilitate localization, which is essential for diagnosis and formulation of an appropriate treatment plan.