Limb salvage surgery has become the preferred practice versus amputation for osteosarcoma of the distal end of the femur since 198617. However, unacceptable walking gait and poor function due to the LLD occur frequently in clinical practice. The consensus on the surgical indications of LLD is lacking, but it is generally believed that <2 cm does not affect the patient's function, 2–4 cm can be corrected by shoe lift, and >4 cm is suggested to be solved by different limb lengthening methods18–20. LLD has been one of the most challenging issues for limb salvage surgery with more patients with osteosarcoma achieving long-term survival21–24. The reasons for LLD can be biological reconstruction failure (bone absorption), prosthesis subsidence due to aseptic loosening, regular prosthesis replacement for immature patients, and so forth. We developed a novel staged lengthening strategy for LLD. While implementing this strategy, only an external fixator and standard static mega prosthesis (two-time honored procedures) were needed. Both hardware were easy to access, and the needed surgical techniques were quite mature. Our early results showed satisfactory LLD correction, favorable functional outcomes, and fewer complications.
Limitations
This study had several limitations. First, our series of nine patients was small. More patients are needed to verify the functional outcomes, LLD correction, and complications. Second, this was a retrospective analysis of patients who received this lengthening strategy. A prospective study with a comparison cohort such as expandable prosthesis replacement would be preferred to compare this technique with other lengthening strategies. However, the unavailability of extendable prostheses in our country currently makes it impossible to perform such clinical studies currently. Nevertheless, we believe that our findings may provide initial evidence that this lengthening strategy has some merit and requires further exploration, even for patients with expandable prostheses available. We think that the preliminary presentation of this strategy may encourage other surgeons to attempt it in clinical practice. Finally, the mean follow-up of 20 months (3–70) (from the third surgery in stage 3) was insufficient to address the long-term complications and functional outcomes associated with this strategy. Nevertheless, we can assume that the long-term outcome should be as in reports using mega prosthesis since they are basically the same after LLD correction.
Functional outcomes
The mean MSTS score of this series at the final follow-up was 96.3% (86.7%–100%), significantly superior to that before the lengthening. The MSTS function was comparable to that in other studies of regular mega-prosthesis reconstruction,25,26 and even better than that in some previous reports27–29. While seeking the reasons for the functional score improvements, it was found that patients suffered greatly from LLD. Leg lengthening improved five of the subsets of MSTS score, including function, emotional acceptance, supports, walking, and gait. Although two patients with total femoral prosthesis replacement showed gluteal gait and limited walking ability, both were quite satisfied with the outcome of the lengthening procedure. Except for the patient with pathologic fractures, most of our patients wore shoe lifts before lengthening. However, 37.5% (3/8) of the patients developed prosthesis breakage, which made it impossible to continue wearing shoe lifts and hence surgery had to be performed. Besides, prosthesis breakage itself was believed to be associated with LLD. The ROM of the current series was lower than that of those who underwent regular mega-prosthesis replacement30. The long-term straight leg may contribute to ROM limitations. Although the designed mean duration from the first surgery to the third surgery (straight leg) was 6 months, it took as much as 12 months eventually due to COVID-19.
LLD correction
The treatment of LLD in adult patients with sarcoma was rarely reported in the literature. Expandable prosthesis, which was designed for skeletally immature patients, was a method of compensating for the overgrowth of the contralateral limb. Only few cases were reported to use expandable prostheses in the adult population12,13,20. Sewell reported nine adults who received noninvasive expandable prostheses. The mean length gained was 56 mm (19–107), requiring a mean of nine lengthening episodes12. In a systematic review of expandable prostheses in skeletally immature patients31, the mean leg lengthening was 4.3 cm, with a mean of 4.4 lengthening procedures. However, the rate of LLD >2 cm was 31% for patients over 16 years in age at the final follow-up. In our series, the leg length gain ranged from 3.6 cm to 15.6 cm with three surgeries. The mean LLD at the last follow-up was 0.3 cm, ranging from –0.3 to 2.1 cm. The current lengthening strategy showed obvious advantages regarding the final LLD correction. Distraction osteogenesis using the external fixator has been reported to correct LLD15,32. However, the distraction was commonly performed on the tibia side, resulting in an elevated knee center compared with the contralateral limb. The impact of the knee center change on gait and function was unknown.
Complications
The complication rate of expandable prostheses remains high. According to a recent systematic review of 292 patients31, the overall complication and revision rate was 43%, increasing to 59% and 89% in patients with more than 5 and 10 years of follow-up, respectively. In the current lengthening process, after the removal of the fixator, the final prosthesis was not introduced simultaneously to prevent the possible spread of infection from the pin sites to the prosthesis. Besides, about 2 cm overcorrection in stage 1 was recommended because acute shortening might be needed during the third surgery to release excessive soft tissue tension and cover the components. We believe that the aforementioned measures may contribute to the early favorable low complication rate. Long-term complications may be anticipated comparable with those of other static mega-prostheses.