Computational evaluation of psoas muscle influence on walking function following internal hemipelvectomy with reconstruction

Abstract

An emerging option for internal hemipelvectomy surgery is custom prosthesis reconstruction. This option typically recapitulates the resected pelvic bony anatomy with the goal of maximizing post-surgery walking function while minimizing recovery time. However, the current custom prosthesis design process does not account for the patient's post-surgery prosthesis and bone loading patterns, nor can it predict how different surgical or rehabilitation decisions (e.g., retention or removal of the psoas muscle, strengthening the psoas) will affect prosthesis durability and post-surgery walking function. These factors may contribute to the high observed failure rate for custom pelvic prostheses, discouraging orthopedic oncologists from pursuing this valuable treatment option. One possibility for addressing this problem is to simulate the complex interaction between surgical and rehabilitation decisions, post-surgery walking function, and custom pelvic prosthesis design using patient-specific neuromusculoskeletal models. As a first step toward developing this capability, this study used a personalized neuromusculoskeletal model and direct collocation optimal control to predict the impact of ipsilateral psoas muscle strength on walking function following internal hemipelvectomy with custom prosthesis reconstruction. The influence of the psoas muscle was targeted since retention of this important muscle can be surgically demanding for certain tumors, requiring additional time in the operating room. The post-surgery walking predictions emulated the most common surgical scenario encountered at MD Anderson Cancer Center in Houston. Simulated post-surgery psoas strengths included 0% (removed), 50% (weakened), 100% (maintained), and 150% (strengthened) of the pre-surgery value. However, only the 100% and 150% cases successfully converged to a complete gait cycle. When post-surgery psoas strength was maintained, clinical gait features were predicted, including increased stance width, decreased stride length, and increased lumbar bending towards the operated side. Furthermore, when post-surgery psoas strength was increased, stance width and stride length returned to pre-surgery values. These results suggest that retention and strengthening of the psoas muscle on the operated side may be important for maximizing post-surgery walking function. If future studies can validate this computational approach using post-surgery experimental walking data, the approach may eventually influence surgical, rehabilitation, and custom prosthesis design decisions to meet the unique clinical needs of pelvic sarcoma patients.

Keywords: computational modeling; internal hemipelvectomy surgery; neuromusculoskeletal modeling; optimal control; orthopedic biomechanics; pelvic sarcoma; predictive simulation; treatment optimization.

FIGURE 1

(A) Sample x-ray image of a pelvic cancer patient who received internal hemipelvectomy surgery with no reconstruction. (B) Sample x-ray image of a pelvic cancer patient who received internal hemipelvectomy surgery with allograph reconstruction and a total hip replacement. Images courtesy of Dr. Valerae Lewis, MD Anderson Cancer Center patient education DVD.

FIGURE 2

Overview of the computational processes used for model personalization and treatment optimization. Top row: Model personalization process. Bottom row: Treatment optimization process.

FIGURE 3

Animation strip comparing the subject’s experimental walking motion (translucent skeleton) to his predicted walking motion when post-surgery operated side psoas strength was 100% of its pre-surgery value (opaque skeleton).

FIGURE 4

Animation strip comparing the subject’s experimental walking motion (translucent skeleton) to his predicted walking motion when post-surgery operated side psoas strength was 150% of its pre-surgery value (opaque skeleton).

FIGURE 5

Experimental pre-surgery and predicted post-surgery joint angles for post-surgery psoas strengths of 100%, and 150% of the pre-surgery value. The gait cycle begins with operated leg heel strike.

FIGURE 6

Experimental pre-surgery and predicted post-surgery joint moments for post-surgery psoas strengths of 100%, and 150% of the pre-surgery value. The gait cycle begins with operated leg heel strike.