CORR Insights®: Compliant Compression Reconstruction of the Proximal Femur Is Durable Despite Minimal Bone Formation in the Compression Segment

Where Are We Now?

Endoprosthetic reconstruction of the femur following either distal or proximal femoral oncologic resection requires stable and durable fixation of the implant into the remaining bone segment. The size of cemented or uncemented stems can vary, but generally both stems range between 10 and 15 cm in length. Cemented or uncemented stems of this size have comparable success rates with respect to stability and implant survival. More recently, surgeons have been using an approach involving a short segment spring mechanism with compliant, self-adjusting compression stem fixation. One advantage of this approach is the ability to achieve fixation in patients where the remaining bone segment is too short to allow for traditional stem fixation. Retrieval studies have demonstrated bone-implant integration [12] and reports on patients who have undergone revision highlight the large amount of bone that can be salvaged given the short length of the stem to be revised [18]. Indeed, some centers employ the compliant compression stems even in instances where the remaining bone segment could accommodate a traditional stem.

Reported case series and retrospective comparative series of distal femur reconstructions [3, 8, 11, 18] have shown comparable medium- to long-term durability of the compression fixation segment relative to other forms of fixation. However, early rotational instability caused by lack of bone ingrowth occurs in approximately 10% of patients [4, 15, 21].

In the current study [5], data from a series of proximal femur reconstructions showed similar results with more than 90% implant-specific survival and fixation at the bone-prosthesis interface despite less-than-expected new bone formation around the compression fixation component. Based on these discoveries, surgeons should note the potential utility of compression fixation stems when reconstructing the proximal femur and understand that new bone formation around the compression stem may not be necessary for implant survival.

Where Do We Need To Go?

Despite the emerging evidence that medium- and long-term fixation durability are satisfactory with compression stem fixation [4, 15, 21], the need to recommend restricted weightbearing for prolonged periods to allow for osseous integration may offset the advantages of this approach. The long-term durability and accelerated rehabilitation programs associated with conventional cemented and uncemented stems in oncologic endoprosthetic reconstruction are encouraging [14, 17], and therefore, the benefit of the compression fixation mechanism may be more appropriately directed at a smaller subset of patients. Christ et al. [5] clearly outline their indications for compression fixation: younger patients, nonirradiated bone, and adequate cortical thickness. This single-center experience is valuable and may be generalizable to other centers and populations. However, only a handful of other centers have reported their experiences with the Compress implant (Zimmer Biomet). Therefore, the population most likely to benefit from compliant compression fixation remains unclear.

Short-term stem loosening events within the first year are concerning and usually result from the implant not osseointegrating. It is not known why the bone grows into some patients’ implants and not others. It is possible that treatment factors such as postoperative chemotherapy may play a role [2]. In addition, the appropriate postoperative weightbearing regimen may need to be adapted to individual patients based on biological factors (patient age and chemotherapy, for example) as well and surgical factors such as length of bone resected and remaining soft tissue and muscle attachments. It is also unclear whether radiographic findings of new bone formation around the compression fixation stem should be used to direct progression in weightbearing status and whether new bone formation should be considered equally important between proximal femoral reconstruction and distal femoral reconstruction [5].

The advantages of the compression fixation stem also need to be clearly delineated. In instances where the remaining bone segment is too short for standard stem fixation, the compression fixation stem is an obvious and suitable solution. The preservation of bone stock through the reduction of stress shielding from longer stems may be critical in patients where subsequent revision comes into the picture. However, do these advantages outweigh, in all patients, the risk for early rotational loosening and the need for prolonged protected weightbearing?

How Do We Get There?

Prospective evaluation of the compression fixation implant in a broad patient population would assist in filling these knowledge gaps. Randomized controlled trials of surgical implants are challenging for many reasons, including the lack of surgeon equipoise in the choice of implant and implant fixation [20]. However, prospective registries have been instrumental in identifying failure mechanisms of implants [16], and the recently initiated Musculoskeletal Tumor Society Registry developed in collaboration with the American Academy of Orthopaedic Surgeons would be the ideal mechanism to achieve this goal is assessing outcomes in compression fixation [1]. Studies on registry data can identify the most common reasons for implant failure [13]. Because registry data represent a large population, the dataset can be powered for multivariate analysis to isolate patient- and treatment-related factors that contribute to the need for implant revision [7].

The Prophylactic Antibiotic Regimens in Tumor Surgery randomized controlled trial collected prospective data on 602 international patients who underwent oncologic prosthetic reconstruction of the femur or tibia. The trial completed enrollment in October 2019 and the final 1-year follow-up at the end of 2020 [9, 19]. The type of implant used for reconstruction was collected as a prospective data point for all patients in addition to all revision surgeries. Therefore, prospective data will be available for all compression fixation implants used in trial participants. Secondary analysis of trial data on revision surgeries and modes of implant failure within the first year postoperatively will shed light on the patient and reconstruction factors associated with the need for revision surgery.

Finally, the leaders in the field who have experience with compliant compression fixation in oncologic reconstruction might create a consensus-based guideline on the indications for the implant, the identification of the appropriate patient population, and the most-effective rehabilitation program. With only retrospective case and cohort series published to date, consensus-based guidelines would provide some direction for surgeons in the short- and medium-term [6]. These guideline panels would require mandatory and explicit conflict of interest declarations as well as unbiased members on the panel that could offset these potential conflicts of interest [10]. Certainly, in situations where stem fixation in endoprosthetic reconstruction must be achieved with only a short remaining bone segment, the compression fixation technique is handy. Recommendations beyond this indication will require further evidence and unbiased consensus-based interpretation of the evidence.