The prosthesis replacement site was the distal femur in 28 and the proximal tibia in 12 cases. Among the 7 cases requiring revision due to stem breakage or loosening, the replacement site was the distal femur in 5 and the proximal tibia in 2. The shortest and longest times until revision for breakage and loosening, after the initial wide resection followed by reconstruction of the tumor affected limb or an elongation-type prosthesis placement, were 10 months and 11 years, respectively, with a mean of 6 years and 2 months.
DF distal femur, PT proximal femur, HMRS Howmedica Modular Resection System, KMFTR Kotz Modular Femoral and Tibia Replacement, PH type 1 physio-hinge type 1, PH type 2 physio-hinge type 2
Based on the above observations, stem size, shape, and porous coating serve as countermeasures against stem breakage, as does bone grafting to the bone stump and preservation of the periosteum [, ]. However, no ideal prosthesis has as yet been established, though many researchers have investigated and developed various promising models . Based on this study, we consider the following points to be important for avoiding prosthetic stem breakage: (1) Minimizing the length of bone resected, i.e., it is desirable not to exceed one third of the affected bone by employing a limited operation, and (2) selection of a stem diameter of at least 12 mm. For the femur, the use of a curved stem should be investigated in consideration of the anatomical shape of this bone.
All stems with a 10-mm diameter are of the Growing Kotz and KMFTR types. In cases reconstructed with the HMRS, stems with a relatively small diameter, 11 or 12 mm, were used in 80%. This may reflect the Japanese physique. The mean resection rate was 34.7% in the non-revision and 45% in the revision cases. The length of resected bone was thus greater in the revision than in the non-revision cases. When the resection rate is almost 45% in the clinical setting, possible reconstruction methods other than the use of a tumor prosthesis include total femoral replacement and biological reconstruction [, , ]. However, these reconstruction methods are indicated in only limited cases. When a tumor prosthesis is used, attention should be paid to the bone resection rate.
The hip prosthesis consists of a specially designed ball that connects to a stem and is inserted into the femur. A prosthetic cup is inserted into the worn socket. The prosthesis has a smooth surface that fits together to allow the ball to move easily and comfortably.
Prosthesis use facilitates the early acquisition of stable functioning of the affected limb, but several complications have yet to be overcome. Breakage and loosening necessitate revision in some cases. Methods considered to reduce the risk of prosthesis breakage, include limiting resection of the affected bone to no more than 30% and adoption of as thick a stem as possible, i.e., with a diameter of at least 12 mm, fitting the anatomical shape of the femur. The unchanged function of the affected limb after revision and instructing of patients to avoid excessive exercise in daily activities are also important for maintenance of prostheses. Although only the elongation-type of Growing Kotz is covered by the national health insurance system in Japan, this prosthesis should also be selected with care, taking the child’s future development into consideration.
The replacement site was the distal femur in 5 and proximal tibia in 2. Revision was performed 6 years and 2 months after the previous prosthesis placement on average. The broken prosthesis model was KMFTR in 4 and HMRS and the physio-hinge type in one each. Revision due to loosening was performed in a case requiring replacement with Growing Kotz prosthesis. The model was switched to HMRS in 3, and the stem diameter was changed to 12 mm in 3 KMFTR breakage cases. The mean stem diameters were 11.2 and 10.2 mm in the non-revision and revision groups. The respective resection rates were 36 and 45%. The mean functional evaluation was 70.1% before and 76.2% after revision.
The components are designed so that metal articulates against plastic, providing smooth movement and minimal wear. The patellar component is a dome-shaped piece of polyethylene that is identical to the shape of the patella and glides in the groove of the femur.Fixed-bearing Prosthesis vs.
To reduce the risk of tumor prosthesis breakage, the amount of bone resection should be limited to 30% or less in the affected bone, the stem diameter should be at least 12 mm, and the stem shape should be fitted to the anatomical shape of the femur.