Commentary & Perspective

Commentary & Perspective on
"Motor Nerve Palsy Following Primary Total Hip Arthroplasty"
by Christopher M. Farrell, MD, et al.

and on
"Early Postoperative Transverse Pelvic Fracture: A New Complication Related to Revision Arthroplasty with an Uncemented Cup"
by Bryan D. Springer, MD, et al.

Commentary & Perspective by
Vincent D. Pellegrini, Jr., MD*,
University of Maryland School of Medicine, Baltimore, Maryland

The Debit Side of Total Hip Arthroplasty; One Step Forward, Two Steps Back?

While few would dispute that the surgical technology associated with total hip arthroplasty has advanced over the past four decades, a provocative few might argue that there has been little to show for all of the "enhancements" on the credit side of the patient ledger. In this issue of The Journal, the matter of complications after total hip arthroplasty is assessed in a context that might lend some credence to the skeptics who question the incremental patient benefit(s) associated with "contemporary" total hip replacement.

Morrey and his colleagues from the Mayo Clinic provide a retrospective chart review of more than 27,000 primary total hip arthroplasties performed since 19701. While the 0.17% prevalence of motor palsy that was observed in 47 of 27,004 hips would at first seem reassuring, a more thorough look reveals some expected as well as surprising observations. Consistent with conventional wisdom, peroneal and sciatic nerve palsies were nearly fifteen times more common than femoral nerve palsies, and limb-lengthening was found to be significantly associated with motor palsy (p < 0.01), albeit by only 0.6 cm more than the matched cohort. Only slightly more than one-third of patients with complete motor palsies recovered fully; their maximal functional return occurred at 21.1 months after operation. In contrast, patients who had only partial and incomplete functional return had a mean maximal functional recovery at two years (range, three months to 6.5 years). Except for one instance in which an evolving hematoma with progressive loss of neurologic function was successfully resolved with surgical decompression, the results of reoperation for motor palsy were unpredictable and inconsistent. Electromyography had little predictive or prognostic value in the assessment of palsies.

Functional results left much to be desired: nearly one-half of patients required a walking aid and one-third used a lower-limb orthosis for ambulation at final review. While logistical regression analysis of a matched patient cohort is arguably of minimal value because it represents only a token sampling of the remaining nearly 27,000 hips, an increased risk of palsy was observed in patients with a diagnosis of posttraumatic arthritis and developmental hip dysplasia. Interestingly, a body mass index of 30 or higher was found not to be associated with a greater risk of nerve palsy.

Most striking, however, was the most powerful statistical association of the entire study; the majority of motor nerve injuries occurred in patients who underwent total hip arthroplasty after 1990 (p = 0.0006). Multivariate regression analysis held this to be true and was further supported by the parallel observation by univariate regression analysis that the use of a cementless femoral component was associated with a statistically greater risk of nerve palsy that was twice that of patients who had a cemented femoral component (p = 0.03).

In the second paper, also from the Mayo Clinic, Springer et al.2 report on a retrospectively identified series of seven patients (1.2%), among 585 acetabular revisions performed between 2000 and 2003, who had sustained a transverse acetabular fracture related to acetabular component revision. The mean time to recognition of the resulting pelvic discontinuity was eight months (range, one to twenty-seven months) after operation. The authors contend that the fractures developed postoperatively during the repetitive cyclic loading of the revision cup because immediate postoperative radiographs did not reveal a fracture of the pelvis. However, one must consider the possibility that the transverse acetabular fractures represent a delayed presentation of what was in fact an intraoperative event. Of particular interest, each of the revision cups associated with fracture was made from tantalum trabecular metal and impacted with a 2-mm to 4-mm press-fit after reaming of the acetabular vault. The tantalum trabecular metal has a high surface roughness that approaches the texture of cancellous bone; indeed, this characteristic may mean that tantalum is particularly poorly suited to under-reaming and a press-fit impaction application in the revision setting. The authors list only one prior report of pelvic discontinuity following acetabular revision associated with an acetabular stress fracture3. Certainly the observation that these tantalum cups were ingrown to bone on one half of the pelvis and not the other is further suggestive of an intraoperative disruption of the adjacent osseous surface before ingrowth had occurred, rather than a late fracture around a well-fixed ingrown socket. One must consider the possibility that this new material, with its greater surface roughness coupled with a press-fit underreamed application, played a causative role in the observed fractures.

Technological advances have provided irrefutable improvements in the field of orthopaedics, yet the introduction of new technology is often accompanied by unintended adverse consequences. The institutional experience of the Mayo Clinic suggests that implantation of cementless hip replacement components was associated with a fourfold greater risk of nerve palsy in the last ten years, and a promising new tantalum material for complex acetabular reconstruction was associated with pelvic discontinuity. If technological advances are not subjected to periodic review, we may find that the success of taking one giant step forward may be overshadowed by the necessity of taking two steps back4.

*The author did not receive grants or outside funding in support of his research for or preparation of this manuscript. He did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the author is affiliated or associated.

References

1. Farrell CM, Springer BD, Haidukewych GJ, Morrey BF. Motor nerve palsy following primary total hip arthroplasty. J Bone Joint Surg Am. 2005;87:2619-25.
2. Springer BD, Berry DJ, Cabanela ME, Hanssen AD, Lewallen DG. Early postoperative transverse pelvic fracture: a new complication related to revision arthroplasty with an uncemented cup. J Bone Joint Surg Am. 2005;87:2626-31.
3. Mahoney CR, Garvin KL. Periprosthetic acetabular stress fracture causing pelvic discontinuity. Orthopedics. 2002;25:83-5.
4. Lazansky MG. Complications revisited. The debit side of total hip replacement. Clin Orthop Relat Res. 1973;95:96-103.