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JBJS Classics: Porous-Coated Hip Components

JBJS Classics Logo.pngOrthoBuzz regularly brings you a current commentary on a “classic” article from The Journal of Bone & Joint Surgery. These articles have been selected by the Editor-in-Chief and Deputy Editors of The Journal because of their long-standing significance to the orthopaedic community and the many citations they receive in the literature. Our OrthoBuzz commentators highlight the impact that these articles have had on the practice of orthopaedics. Please feel free to join the conversation by clicking on the “Leave a Comment” button in the box to the left.

In their classic 1987 publication, Drs. Charles Engh, Dennis Bobyn, and Andrew Glassman described clinical and radiographic results of a series of 307 hips with 2-year follow-up, and 89 hips with 5-year follow-up after total hip arthroplasty in which the patients had received an extensively porous-coated femoral stem. The authors also described histologic evaluation of 11 hips retrieved at autopsy or revision.

By 1987 the same authors as well as other investigators had already published observations concerning the influence of femoral stem size, shape, stiffness, and porosity on clinical and radiographic evidence of fixation and stress shielding in humans and animal models.1,2 But this study, which so far has been cited more than 1500 times, goes “above and beyond” by carefully correlating previous observations with histologic sections obtained through human femora.

Among other achievements, Engh et al. described radiographic criteria for categorizing a femoral implant as either stable by bone ingrowth, stable by fibrous tissue ingrowth, or unstable. Implants thought to be stable by fibrous ingrowth had a prominent radio-opaque line around the stem, separated from the implant by a radiolucent space up to 1 mm in thickness. This line was thought to represent a shell of bone with load-carrying capability. However, histology demonstrated that the space between the shell and the implant was composed of dense fibrous tissue. When the shell was present, there tended to be little hypertrophy or atrophy of the adjacent femoral cortex.

Engh et al. noted that radiographs and histology of hips with extensive ingrowth from the endosteum often showed parallel increased porosity of the adjacent cortex – an early manifestation of stress shielding. Overall, 259 (84%) of the femoral stems had radiographic findings suggestive of bone ingrowth, 42 (13%) had findings interpreted as stable fibrous ingrowth, and 2% were thought to be unstable (but not yet revised at the time of the study). Stress shielding was much more common in larger-diameter stems and those with good bone ingrowth compared to smaller implants or those with stable fibrous fixation.

Why do we consider this manuscript a classic? First, the authors include a careful correlation of histology with radiographic and clinical findings, helping illustrate the importance of tight press fit at the isthmus to achieve proximal fixation. The authors also document intracortical porosity as the morphologic manifestation of stress shielding and emphasize the impact of a small increase in stem diameter on axial rigidity.

Designs of femoral stems have evolved considerably since the 1980s,3 and the findings described in this paper helped validate fundamental principles related to load transmission and bone remodeling4-6 and thus helped advance that evolutionary process.

Thomas W. Bauer, MD, PhD
JBJS Deputy Editor

References

  1. Bobyn JD, Pilliar RM, Binnington AG, Szivek JA. The effect of proximally and fully porous-coated canine hip stem design on bone modeling. Journal of orthopaedic research : official publication of the Orthopaedic Research Society 1987;5:393-408.
  2. Bobyn JD, Pilliar RM, Cameron HU, Weatherly GC. The optimum pore size for the fixation of porous-surfaced metal implants by the ingrowth of bone. Clinical orthopaedics and related research 1980:263-70.
  3. McAuley JP, Culpepper WJ, Engh CA. Total hip arthroplasty. Concerns with extensively porous coated femoral components. Clinical orthopaedics and related research 1998:182-8.
  4. Huiskes R. Validation of adaptive bone-remodeling simulation models. Stud Health Technol Inform 1997;40:33-48.
  5. Huiskes R, Weinans H, Dalstra M. Adaptive bone remodeling and biomechanical design considerations for noncemented total hip arthroplasty. Orthopedics 1989;12:1255-67.
  6. Weinans H, Huiskes R, Grootenboer HJ. Effects of fit and bonding characteristics of femoral stems on adaptive bone remodeling. J Biomech Eng 1994;116:393-400.

JBJS Case Connector Debuts Whole-Slide Images

WSI_Image_2016-10-04.png It is not often that readers of scholarly journals have a “Wow!” moment, a chance to be unexpectedly delighted by a new discovery.1 In the September 14, 2016 edition of JBJS Case Connector, Zhang et al. provide readers of the JBJS family of journals the first of what we hope will be many such moments: the ability to link to and navigate a digital, whole-slide image (WSI) of an entire microscope slide.

Fig_1_for_WSI_OBuzz_2016-10-04_1533.png

Figure 1

Illustrating the histology of tumors and the tissue-level details in basic science studies has long been a challenge. Until recently, readers were usually subjected to the few fields of view that the author chose to photograph. The more senior among you may remember with nostalgia attempting to make sense of fuzzy, black-and-white, circular, histology images viewed as if seen through an antique monocular microscope (Fig. 1).  The advent of color printing (often at the author’s extra expense) and eventually digital photographs improved somewhat the quality of each image, but readers were still required to accept that the author had selected fields of view that were truly representative of the subject matter.

In their case report titled “Morphological Transformation of Giant-Cell Tumor of Bone After Treatment with Denosumab,” Zhang et al. include two links to whole-slide images. In the first, readers can link from a conventional digital photograph of a core needle biopsy to the whole-slide image of the giant cell tumor. The authors also include several conventional photographs of the tumor after resection, along with a link to the corresponding scanned microscope slide.

The use of a viewing algorithm similar to that used by Google Earth allows readers to navigate and zoom in on not just the few isolated fields of view selected by the authors, but the hundreds to thousands of additional fields contained in the original microscope slide of this complicated tumor. While it’s very helpful for illustrating tumor histology, we anticipate that WSI technology will be even more valuable when applied to basic science studies of fracture healing or cartilage, nerve, and tendon repair—as well as many other possible applications.

Thomas Bauer, MD
JBJS Case Connector Co-Editor

Reference

  1. Glassy EF, Rebooting the Pathology Journal. Learning in the Age of Digital Pathology. Archiv Pathol Lab Med 2014;138:728-729.