Biomedical Engineering Reference
In-Depth Information
size of polyethylene debris, osteolysis around a total knee joint is less frequent than in a total hip
replacement.
10.3.3 Ankle Joint Replacement
Total ankle replacements had not met with as much success as total hip and knee replacements, and
typically loosened within a few years of service (Claridge et al. 1991; Guyer and Richardson 2008; Durr
2009; Coetzee and Deorio 2010). This was due, presumably, to the high load transfer demand over the
relatively small ankle surface area and the need to replace three articulating surfaces (tibial, talar, and
fibular). The joint configurations that have been used are cylindrical, reverse cylindrical, and spherical.
The materials used to construct ankle joints are usually Co-Cr alloy and UHMWPE. Degeneration of
the ankle joint is currently treated with fusion of the joint, since prosthesis for total ankle replacement
is considered to be in intermediate stages of development. The current outcomes have improved and the
trend suggests that they will approach, in the future, those of total hip and knee replacement (Fevang
et al. 2007). Figure 10.10a shows ankle and other total joint replacements.
10.3.4 Shoulder Joint Replacement
The prosthesis for total shoulder replacement consists of a humeral and a glenoid component (Figure
10.10b). Like the femoral stem, the humeral component can be divided into head, neck, and shaft.
Variations in the length of the neck result in change in the length of the extremity. Even though the
patient's perception of length of the upper extremity is not as accurate as that of the lower extremity,
varying lengths of the neck are used to fine-tune the tension of the soft tissues to obtain maximal stabil-
ity and range of motion (Wiater and Fabing 2009).
The shoulder has the largest range of motion in a body, which results from a shallow ball-and-socket
joint, which allows for a combination of rotation and sliding motions between the joint surfaces. To
compensate for the compromise in congruity, the shoulder has an elaborate capsular and ligamentous
structure, which provides the basic stabilization. In addition, the muscle girdle of the shoulder provides
additional dynamic stability. A decrease in the radius of curvature of the implant to compensate for soft
tissue instability will result in a decrease in the range of motion (Neer 1990).
FIGURE 10.10
Miscellaneous examples of prostheses for total joint replacement: (a) ankle, (b) socket-ball shoul-
der joint, (c) hinged elbow joint, (d) elastomer finger joint, and (e) spine disk.
