Volume 5, Number 2 ISSN 2331-2262 (print) • ISSN 2331-2270 (online) The Incidence of Dislocation Utilizing a Neck Sparing Stem in Primary THA in Community Based Practices with the Posterior Approach McPherson E 1, Vaughn B 2, Keppler L3, Brazil D 4, McTighe T 5 This study retrospectively reviews the clinical results of a novel proximal neck-sparing cementless prosthesis for primary Total Hip Arthroplasty (THA). This neck-sparing prosthesis preserves the entire circumference of the femoral neck. The porous coated surface is located only within the femoral neck region. This study group included 338 primary THA's from three institutions. All approaches and tech- niques were similar, using a postero-lateral approach in all cases. Average follow-up was 38 months (range 12-56 months). There were five stem revisions (1.5%) in this group. Two stems were revised for aseptic loosening, two were revised for recurrent dislocation, and one was revised for a chronic peripros- thetic infection employing a two-stage protocol. We had 3 dislocations (0.88%) and all three had re-op- erations. The neck sparing prosthesis is alluring as it saves almost the entire femoral neck and requires minimal deep posterior soft tissue releases. Our dislocation rate in this series was low. Insertion of a neck sparing prosthesis requires fastidious preparation and gentle insertion, but we find this design to provide reliable clinical function at short-term follow-up.
Keywords: THA, hip, arthroplasty, posterior approach, dislocation, neck sparing, and risk factors, primary
Level of Evidence: AAOS Therapeutic Level III
1 LA Orthopedic Institute, 201 S. Alvarado Street, Suite 501, Los Angeles, CA 90057 US 2 Raleigh Orthopaedic Clinic, 1325 Timber Drive East Garner, NC 27529 US3 St. Vincent Charity Medical Center, 6701 Rockside Rd #100, Cleveland, OH 44131 US4 Signature Orthopaedics, 7 Sirius Rd Lane Cove West NSW AU Total hip arthroplasty (THA) is one of the most effec- 5 Joint Implant Surgery & Research Foundation, 46 Chagrin Shopping Plaza, #117, Chagrin Falls, OH tive orthopedic procedures, providing consistently high success rates across all population segments—as mea- sured by pain relief, improved function, and patient sat- 2015 McPherson, Vaughn, Keppler, Brazil, McTighe. All rights reserved isfaction [1,2,3,4,5]. As a result of these good outcomes, Authors retain copyright and grant the journal right of first publication with the work. THA indications have been expanded to include young- . This license allows anyone to download works, build upon the mate- er and more active patients [6,7]. However younger pa- rial, and share them with others for non-commercial purposes as long as they credit the senior author, Reconstructive Review, and the Joint Implant Surgery & Research tients are more likely to need revision surgery, and compli- Foundation (JISRF). An example credit would be: "Courtesy of (senior author's name), cations are higher with revision THA procedures [7,8,9]. Reconstructive Review, JISRF, Chagrin Falls, Ohio".
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14 JISRF • Reconstructive Review • Vol. 5, No. 2, July 2015
With the increased likelihood that younger patients will re- of surgical implantation quire a revision surgery later in life, it is advantageous to (Figure 4). Limited weight maximize proximal femoral bone stock to provide as much bearing was advocated for bone as possible for revision stem implantation [10]. Pres- the first 4-6 weeks since ervation of the entire femoral neck using a neck sparing the porous coating is limit- prosthesis is a newer surgical technique that started in Italy ed to the proximal portion and has now been widely used in the last decade [11,12]. of the stem that engages Neck sparing implants potentially have the advantage of with the femoral neck.
less thigh pain and are helpful to the surgeon when using a The ARC stem design small incision approach. In addition, there is a mechanical features a short curved ti- advantage in retaining the femoral neck which results in a tanium alloy stem with a reduction of torsional forces placed on the implant / bone novel conical flair for en- Figure 4. Intraoperative X-Ray Showing interface [1,13] (Figure 1). hanced proximal compres- Trial Rasp with Trial head/Neck and Cup One potential problem with re- sive loading of the medi- in Place. (Courtesy JISRF Archives) taining a majority of the femo- al calcar (Figure 5). The ral neck is there is a chance for proximal third of the stem boney impingement. This can Figure 1. has commercially pure ti- lead to residual pain, dysfunc- Illustration tanium plasma spray coat- tion, and possible dislocation. Showing a Short ing with a surface layer of In this study we review the ear- Curved Neck- Sparing Style Stem hydroxyapatite (HA) coat- ly clinical results utilizing a ce- (Courtesy Declan ing (25μm) to promote an mentless proximal coated neck early biologic bone healing Figure 5. Illustration Showing the Proximal Conical flair of the Stem sparing femoral stem prosthesis. We wanted to assess our to the implant. The modu- Designed to Provide Compressive dislocation rate and clinical results from multiple surgery lar femoral neck is made of Loading to the Medial Calcar of the Stem. (Courtesy JISRF Archives) centers, all utilizing a postero-lateral surgical approach.
cobalt chromium alloy and allows for intra-operative adjustment of joint stability, leg length and offset [15] (Figure 6).
Material and Methods
Between April 2010 and June 2014 we performed 338 short-curved neck-sparing stems (ARC™ Stem, Omni, E. Tauton, MA) (Figure 2). The three se- nior authors (surgeons) utilized Figure 6. Picture of ARC™ Stem Showing Modular Necks in various the postero-lateral approach on positions (Valgus, Neutral & Versus) Co-Cr-Mo, Ceramic Head Taper 12/14, Titanium Alloy Stem with Proximal Porous Pure Titanium all cases [14]. All three surgeons Plasma Spray Coating with a Surface Layer of HA Coating. (Courtesy along with the two additional co- JISRF Archives) authors were all involved with the Figure 2. Illustration Showing All acetabular components were a variety of cementless early development of both the stem ARC™ Neck-Sparing Stem titanium alloy porous coated hemispherical designs and and instrumentation. Preoperative (Omni, E. Tauton, MA) bearing surfaces. All head diameters were restricted to 32 training with cadav- mm or larger. In the smaller patient profile, if a 32 mm head er workshops was a size could not be reached, a dual mobility style implant requirement prior to was chosen. Early in this series two of our surgeons used any clinical surgical a limited number of large metal on metal (MoM) bearings. evaluation of this The MoM bearing was discontinued due to rising concerns device (Figure 3). in the market with this type of bearing surface [16]. A total Intra-operative x- of 77 dual mobility acetabular components were used with rays or fluoroscopy 66 being the Active Articulation design (Biomet, Warsaw, were also required IN) (Figures 7a, & b). The dual-mobility concept utilizes in the early stage Figure 3. Cadaver Work Shop. (Courtesy JISRF a 28mm femoral head that articulates and is locked into a Joint Implant Surgery & Research Foundation •

The Incidence of Dislocation Utilizing a Neck Sparing Stem in Primary THA in Community Based Practices… 15 large polyethylene head. The large polyethylene bearing serves as a large head bearing that articulates within the all-metal monolithic cup.
Figure 7a. Picture of a dual mobility acetabular component (Active Articulation, Biomet, Warsaw, IN) Figure 9b. Picture Showing Rasp Figure 9c. Rasp and Femoral Shaping Medial Femoral Curve Stem Comparing Medial to Stem Shape. (Courtesy JISRF Curvature of the Stem. Figure 7b. Postoperative X-Ray (Courtesy JISRF Archives) Showing ARC Stem with a Dual Mobility Cup. Notice Tight Femoral is gentile and broaching is performed with a small mallet Canal (Dorr I) Distal Slot Pinched with frequent light impactions. Trialing of implants is per- In. (Courtesy Keppler) formed with modular neck trials to optimize hip length, hip offset, and hip stability. Once definitive hip implants have Surgical Technique for Neck Sparing Prosthesis
been placed a meticulous posterior closure is performed. The hip capsule is closed as a separate layer. In all cases The neck sparing femoral stem essentially retains the the hip capsule was closed from the superior acetabulum femoral neck in its entirety up to the upper ¼ neck re- down to the prosthetic femoral neck. In some cases, where gion. Using the postero-lateral approach to the hip, the su- possible, the entire hip capsule was closed. The proximal perior one-half of the short external rotators are released short external rotators are repaired to the posterior greater from the posterior greater trochanter down to the base of trochanter with sutures placed into bone. All soft tissues the femoral neck. The capsule is preserved with transverse are anatomically closed as best possible. incisions made at the acetabular rim and the base of the femoral neck. A longitudinal capsu- lar incision is made in between. This creates anterior and posterior capsu- lar flaps that can be repaired at clo- In our combined series there were 338 implanted short sure. Once the hip is dislocated, the curved neck-sparing stems. Fifty-nine percent of patients femoral neck is resected 5 to 10 mm were female and 41% were male. At an average follow-up below the subcapital junction with a of 38 months (range 12-56 months), Harris Hip Scores av- fine-toothed saw (Figure 8). The neck eraged 91.2 (range 78-100). There were three dislocations cut is based upon preoperative and Figure 8. Illustration Showing Neck Resection in this series (0.88%), all of which required revision sur- intra-operative templating to restore Zones. Zone B being 5-10 gery. In one case, the modular neck was exchanged to add head center of rotation. The neck mm as recommendation . 3.5mm in length and the acetabular polyethylene liner was sparing stem design and instrumenta- (Omni Surgical Technique) also exchanged to add a 15º posterior hood. The stem was tion is based upon following well fixed and retained. In the two other cases, the femo- the native medial curvature ral stems were revised to conventional length stems, along of the proximal femoral neck with exchange of the modular acetabular polyethylene to (Figures 9a, b, & c). Since the add a posterior hood.
femoral neck cortical bone There were five stem failures in this study group. As is distinctly thinner than the Figure 9a. noted above, two stems were revised for recurrent disloca- cortical femoral shaft, prep- Illustration Showing tion (0.6%). In both cases the femoral stems showed sta- aration of the proximal fe- Medial Femoral Curve. (Courtesy ble boney integration and were removed without difficulty. mur is more delicate. Rasping JISRF Archives) Two stems have been revised for aseptic loosening (0.6%). Joint Implant Surgery & Research Foundation 16 JISRF • Reconstructive Review • Vol. 5, No. 2, July 2015
They were both converted to conventional length primary healthcare system [18,19]. About 45% of dislocations oc- hip stems. One stem was removed for chronic periprosthet- cur within 4 weeks of surgery [19]. Various risk factors ic infection utilizing a two-stage protocol (0.3%). The stem such as surgical approach, cup position, combined cup and was easily removed by making a circumferential femoral stem anteversion, and femoral head size can impact clini- cal outcomes. However, the data supporting this view does not include more recent changes in surgical technique and implant technology. Recent changes that have reduced dis- location rates include careful preoperative templating to recreate joint center of rotation, neck-sparing implants that require little in posterior soft tissue releases, and finally minimal (Fig- Figure 10. Retrieved ARC Stem with Good Bone Attachment techniques that emphasize a complete posterior soft tissue ure to Proximal Porous Coating. (Courtesy JISRF Archives) overall revision stem rate in this series was 1.5%. There Restoration of hip mechanics is vital to providing op- was also one acetabular cup revision for aseptic loosen- timal hip function and stability. Careful preoperative ing in this series. In this case, the modular femoral neck templating allows the surgeon to determine appropriate was removed and exchanged in order to facilitate acetabu- reaming depth for the acetabulum. Furthermore, careful lar exposure (Figure 11).
templating determines lateral hip offset and vertical length as referenced from hip center. Preoperative templating fa- cilitates intra-operative assessment and bone preparation for placement of THA implants. Even through preopera- tive templating is important, intra-operative templating with femoral neck measuring jigs must be utilized to cor- roborate preoperative measurements. Hip templating may provide false values especially when the arthritic hip is contracted into external rotation. In this position the femo- ral neck can appear more valgus and vertical. Offset can be underestimated as much as 7 to 10 mm depending on the rotation of the femur when an AP radiograph is used for templating [20,21].
Intra-operatively, trialing of implants is utilized to as- Figure 11. Picture of Explanted Modular Neck. No signs of Corrosion. (Courtesy JISRF Archives) sess hip center, femoral offset, and neck length. Range of motion testing with trial implants is then required to deter- In this series we were able to examine the seven mod- mine combined anteversion of the cup-stem construct. For ular necks that were either revised or exchanged. Even optimum range and stability, combined anteversion should though these cases were revised relatively early in the life be between 35 and 45 degrees [22]. Trialing is also per- cycle of these implants, we observed no signs of corrosion formed to assess for boney impingement tested at end flex- between the modular femoral neck and the femoral stem ion with internal rotation as well as at end extension with external rotation. All impinging osteophytes and excess bone must be removed to maximize hip range without im- pingement and levering. Leg lengths must also be checked. Soft tissues are lax with a shortened leg and this makes the hip more prone to dislocation.
In the last decade there has been a push towards utiliz- Short neck sparing stems are a new ing the anterior hip approach for THA [17]. Advocates of concept to the modern design arma- this approach have criticized the posterior approach for its mentarium of hip implants in North higher rate of dislocation. Historically dislocation results America [1,23]. European surgeons in the posterior approach (with complete detachment of have been working with these stems Figure 12. the external rotators) varied between (4.8% to 7%). Revi- since the early 1980's, beginning with Illustration of Pipino Style Neck- sion surgery for recurrent dislocation has a significant im- the pioneering work of Pipino in Ita- Sparing Stem. pact upon patient morbidity and psychological stress. Fur- ly [1,11,12] (Figure 12). The majori- (Courtesy JISRF thermore, it imparts a significant financial burden on the ty of European neck-sparing stems are Joint Implant Surgery & Research Foundation • The Incidence of Dislocation Utilizing a Neck Sparing Stem in Primary THA in Community Based Practices… 17 novel in that they preserve the entire circumference of the version (Figures 13, 14, & femoral neck and the implants follow the native curve of 15). Recent literature has the proximal femoral neck. In contrast, in North America cast disparaging results the newer short stem designs are just truncated versions of with modular necks in pri- conventional style stems that cut into the proximal femoral mary THA stems [24,25]. neck and still load the femur in the metadiaphyseal region. These reports impugn the The advantages of using short neck-sparing implants are modular neck junction as a several. First, nearly all of the proximal bone is preserved. source of debris from trap- This is advantageous when revision surgery is required. per junction abrasion, fret- Removing a neck sparing prosthesis is facile and the revi- ting and corrosion. This sion stem required is similar to using a conventional pri- debris is a source for creat- mary hip implant. More importantly, the exposure for the ing a toxic reactive synovi- neck sparing prosthesis requires only small deep tissue re- tis that can ultimately lead leases, preserving the deep tissues. This allows for a more Figure 15. Postoperative X-Ray Showing to pseudotumor formation robust posterior soft tissue repair. This is key to minimiz- ARC Stem with a Varus Modular Neck [26]. Biomechanical stud- ing hip dislocation with the posterior approach. Finally, hip Position. (Courtesy JISRF Archives) ies demonstrate that for ev- offset and neck-length are easier to restore. The neck-spar- ery 1mm increase of lateral offset from hip center, there is a ing prosthesis follows the native curve of the femoral neck 8% increase in torque placed upon the modular neck junc- rather than fitting into the medullary canal of the femur. By tion. Furthermore, for every 1mm increase in vertical off- following the femoral neck it is far easier to restore native set from hip center, there is a 6% increase in torque placed femoral offset and neck length. This is a key advantage upon the modular neck junction (Figure that we feel enhances hip stability. With this surgical tech- when using a conventional stem seated into the medullary nique it is easier to gauge soft tissue tension as there has diaphyseal canal, the modular neck junction is far from the been minimal releases of soft tissues compared to the larg- er style approaches and releases needed for implantation of conventional stem designs. This study strengthens our commitment to utilizing a short curved neck-sparing stem when possible. Our overall dislocation rate was 0.88%, which is encouraging. Despite using this stem design in highly active patients, our overall stem revision rate is acceptable at 1.5%.
One caveat with this implant design is the use of the modular femoral neck. Even though much of the femo- ral neck was preserved we still used a modular proximal neck to fine tune offset and Figure 16a Chart Showing Torque Values for Femoral Offset and Neck Length. (Courtesy Ian Clarke) hip center and torque forces upon the junction are high. In contrast, with the neck sparing hip prosthesis the modular neck junction, by virtue of preserving the femoral neck, is much closer to the hip center and modular neck stresses are significantly lower. This has been demonstrated in fi- nite elemental analysis [27,29] (Figure 16b). This is also confirmed in this clinical study. In our 5 retrieved femoral stems we did not visualize any corrosion of the modular taper junction.
In summary, when using the neck sparing femoral stem we advocate head sizes between 32 to 36 mm. Neck skirts Figure 13. Postoperative X-Ray Showing Figure 14. Postoperative X-Ray Showing ARC Stem with a Valgus Modular Neck ARC Stem with a Neutral Modular Neck on the modular femoral heads are to be avoided at all costs. Position. (Courtesy JISRF Archives) Position. (Courtesy JISRF Archives) We do not recommend a modular head greater than 36mm Joint Implant Surgery & Research Foundation 18 JISRF • Reconstructive Review • Vol. 5, No. 2, July 2015
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as this can increase the torque loads upon the modular fem- 8. Haveri S, Uppin RB. Results of Uncemented Total Replacement Done in Very Young oral neck junction. For small acetabular sockets, the dual Patients. Int Surg J. 2014 Aug; 1 (2):80-83 pISSN 2349-3305 eISSN 2349-2902 9. Dorr LD, Luckett M, Conaty JP. Total hip arthroplasties in patients younger than 45 articulation bearing is an acceptable alternative that pro- years. A nine- to ten-year follow-up study. Clin Orthop Relat Res. 1990;(260):215– vides a large head for stability. The majority of motion of 10. McTighe T, Brazil D, et al. The Science Behind a Short (Neck Preserving) Curved the dual mobility construct is through the small 28mm ball Stem Total Hip Replacement. Poster ID: EFFORT 14-4564, June 2014 London, UK.
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sion surgery is needed. We emphasize that there is a dis- 16. Keppler L, McTighe T, Brazil D, The Role of Stem Modularity for THA in a Com- tinct learning curve to preparing and fitting a prosthesis in munity Based Practice. RR, Vol2, No2 (August 2012) P16-26, DOI: a completely intact femoral neck compared to a conven- 17. McTighe T, Mayor M, Stulberg B, Donaldson T, Keggi J, Keppler L, Clarke I, tional diaphyseal engaging cementless stem. Preparation is McPherson E, Interview on Metal on Metal Bearings. RR, Vol 2, No 2 (August fastidious and we strongly encourage the surgeon to attend 18. Matta JM, Shahrdar C, Ferguson T. Single-Incision Anterior Approach for Total Hip a cadaver workshop and/or visit an experienced surgeon Arthroplasty on an Orthopaedic Table. Clin Orthop Rel Res. 2005; 441: 115-24.
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24. McTighe T, Woodgate I, Turnbull A, et al. A New Approach To Neck-Sparing THA Stem. AAOS Poster Exhibit 32, March 2008, San Francisco, CA. DOI: 25. Berry DJ. Utility of Modular Implants in Primary Total Hip Arthroplasty. The Jour- nal of Arthroplasty 29 (2014) 657-658 26. McTighe T, Brazil D, Bruce W. Metallic Alloys in Total Hip Arthroplasty. In: Cash- man J, Goyal N, Parvizi J, eds. The Hip: Preservation, Replacement and Revision. Baltimore, MD: Data Trace Publishing Company; 2015:14-1—14-12.
27. Hsu A, Gross C, Levine B. Pseudotumor From Modular Neck Corrosion After Ce- ramic-on-Polyethylene Total Hip Arthroplasty. Am J Orthop. 2012;41(9):422-426. Figure 17. Postoperative X-Ray Showing Bilateral Hips. Left Showing a 1986 S-Rom 28. Brazil D, McTighe T. Taper Issues in THA. Oral Paper ICJR, Sydney, Australia- Design and the Right Showing a 2010 ARC neck-Sparing Short Curved Stem Design. Both hips are in Place and Functioning Well. (Courtesy Keppler) 29. McPherson EJ, Sherif SM. In Vivo Dissociation of a Dual Articulation Bearing in Revision THA: A Case Report. Journal of Reconstructive Review. 2012; 2(2): 72-76. 30. Brazil D, McTighe T, et al. FEA Analysis of Neck-Sparing Versus Conventional One or more of our authors have disclosed information Cementless Stem. RR October 2011. DOI: that may present potential for conflict of interest with this work. For full disclosures refer to last page of this journal.
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