Shape Analysis of the Patellar Bone Surface and Cutting Plane for Knee Replacement Surgery.

Geometry of the patella (kneecap) remains poorly understood yet is highly relevant to performing the correct patellar cut to reduce pain and to improve function and satisfaction after knee replacement surgery. Although studies routinely refer to "parallel to the anterior surface" and "the patellar horizon," a quantitative definition of these is lacking and significant variability exists between observers for this irregularly-shaped bone. A 2D-3D shape analysis technique was developed to determine the optimal device configuration for contacting the patellar surface. Axial and sagittal pseudo-X-rays were created from 18 computed tomography (CT) scans of cadaveric knees. Four expert surgeons reviewed three repetitions of the X-rays in randomized order, marking their desired cut plane and their estimate of the anterior surface. These 2D results were related back to the 3D model to create the desired plane. There was considerable variability in perceptions, with intra- and intersurgeon repeatability (standard deviations) ranging from 1.3° to 2.4°. The best configuration of contact points to achieve the desired cutting plane was three pegs centred on the patellar surface, two superior and one inferior, forming a 16 mm equilateral triangle. This configuration achieved predicted cut planes within 1° of the surgeon ranges on all 18 patellae. Implementing this, as was done in a subsequent prototype surgical device, should help improve the success and satisfaction of knee replacement surgery.

The efficacy of tourniquet release in blood conservation after total knee arthroplasty.

One hundred consecutive primary total knee arthroplasties performed by a single surgeon were prospectively randomized into two groups to study the effect of tourniquet release for hemostasis on postoperative blood loss and transfusion requirements. The two groups were comparable. Variables such as antiinflammatory drug use; anesthetic; soft-tissue release; and component fixation were analyzed. There was no significant difference between the groups in terms of perioperative blood loss, decrease in hemoglobin or hematocrit level, transfusion need, or incidence of wound or thromboembolic complications. Tourniquet release for hemostasis is not an effective means of limiting postoperative blood loss or reducing transfusion need after primary total knee arthroplasty.

Ingrowth surfaces. Plasma spray coating to titanium alloy hip replacements.

Plasma spray coatings on titanium alloy total hip replacements (THRs) provide a viable alternative to sintered bead or diffusion-bonded fiber metal ingrowth surfaces. The plasma spray process enables the titanium alloy implant to retain 90% of its fatigue strength, as opposed to less than 50% for sintered or diffusion-bonded cementless devices. Laboratory and clinical evidence suggest that plasma spray cementless THRs perform as well, if not better, than other cementless implants. Clinical trials have demonstrated the superiority of a plasma spray cementless THR (Mallory-Head) over a sintered bead cementless THR (PCA) and the equivalent results to a cemented THR. Plasma spray coatings on titanium alloy hip replacements provide a safe, predictable coating for cementless fixation of THRs in the short to medium range of follow-up periods.

Thigh pain in cementless total hip arthroplasty. A comparison of two systems at 2 years' follow-up.

Cementless total hip arthroplasties using 110 porous-coated anatomic (PCA) and 105 consecutive Mallory-Head (MH) prostheses were reviewed using prospectively gathered clinical data and a detailed radiographic analysis. In an earlier experience with the PCA, 13% of patients experienced thigh pain at 1 year and 23% at 2 years. Positive radiographic correlates with thigh pain included subsidence, distal cortical hypertrophy, a tight diaphyseal fit, and stem tip sclerosis. In the current MH study group, the incidence of thigh pain was 7% at 1 year and 3% at 2 years. No radiographic findings correlated positively with thigh pain. The results of this short-term clinical comparison suggest that a long, straight, tapered design offered better initial stability than its anatomic counterpart as reflected in the much lower incidence of thigh pain. These results may translate into improved osseous integration and long-term success.