Modular acetabular cup system provides versatility and positive results

The Pinnacle® Hip System (DePuy Orthopaedics, Inc.) was the first cementless acetabular cup to feature a design allowing varying combinations of acetabular liners. Though other designs have since mimicked this approach, Pinnacle has been established as a class leader and an extremely reliable clinical device. Within my clinical practice over the past 10 years, I have implanted more than 3,000 of these acetabular cups, and I continue to use it for all total hip arthroplasty (THA) patients, both primary and revision.

The variable liner cup system allows surgeons to use Pinnacle on almost every patient that requires a THA. In older patients, for example, a polyethylene liner may be the most appropriate bearing choice. In high-demand patients, a hard-on-hard bearing (ceramic-on-ceramic, ceramic-on-metal, metal-on-metal [MoM]) may be the best choice. The variable liner cup also allows for simplified reoperations in the event a revision is required. In fact, there is no need to replace the entire cup when a liner can easily be switched out to accommodate other designs—lipped, lateralized or face-changing liners—in cases of instability. The Pinnacle Hip System uses Variable Interface Prosthesis taper technology to allow for multiple liner options. Additionally, Pinnacle enables me to refine a single surgical technique with which I am very familiar, and one that has provided consistently positive results for my patients. This has the potential to minimize any variability in outcomes that could be introduced by adopting different implant systems, which I would use less frequently, for different patients.

Clinical data and outcomes


The clinical data on Pinnacle suggest a device that rarely runs into problems. In a study presented at the 2007 AAOS meeting in San Diego, 5-year mid-term results with Pinnacle had a 99.9% survival of the acetabular component.1

Updated results of this study indicate an 8 year survivorship of 96.1% for revision of any component for any reason.2 For reference, the 5 year survivorship is 97.2%. The study included 1,582 primary THAs, performed across 17 surgeons, and involved nine different cemented and uncemented stems. This versatility suggests an implant that is highly adaptable to surgeon experience and compatible with varying surgeon stem philosophies. There were a total of 31/1,582 (1.6%) hips revised for any reason resulting from dislocations (13), deep infections (8), hip pain (1), femoral fractures (3), hematomas (1), adverse local tissue reaction (3) and stem loosening (2). In 10/31 (32.3%) instances the cup was retained and the liner was exchanged with another of the system’s options."The clinical data on Pinnacle suggest a device that rarely runs into problems.... 8-year survivorship of 96.1%."

— Kirk A. Kindsfater, MD

The mean Harris Hip Scores were excellent going from a preoperative score of 46 to a 1-year postoperative score of 95. The mean Harris Hip Scores remained high (range of 94 to 95) throughout 8 years post-operatively. The mean flexion scores were 89° pre-operatively, and 101° throughout 8 years postoperatively. In the study showing 96.1% mid-term survival of the Pinnacle Acetabular Cup System, the cohort was split between the various liner options. Of the total 1,582 hips, 888 (56.1%) received a metal-on-polyethylene (MoP) bearing, 667 (42.2%) received a metal-on-metal (MoM) bearing, and the remaining 27 (1.7%) received a ceramic-on-polyethylene (CoP) bearing.

The MoM group reported 10 failures. Survivorship at 8 years is 96.3% (95 Cl 91.8% to 98.3%) and at 5 years survivorship is 97.5% (95% Cl 94.8 to 98.8%). The following reasons for revision were reported: dislocation (1), deep infection (4), pain (1), femoral fracture (1), and adverse local tissue reaction (3). Three revisions required removal of the Pinnacle Cup."Mid-term results on 236 Pinnacle standard polyethylene and 854 Pinnacle cross-linked polyethylene hips showed, overall, higher survivorship for both cohorts out to 8 years of follow-up...There were no cases of revision due to aseptic loosening, wear or osteolysis."

— Kirk A. Kindsfater, MD

There were 21 failures reported in the MoP group, yielding an 8-year survival rate of 95.8% (95% CI 93.0% to 97.5%). Survivorship at 5 years is 96.9% (95% CI 95.0% to 98.1%). The following reasons for revision were reported: dislocation (12), deep infection (4), aseptic loosening of the stem (2), femoral fracture (2), and hematoma (1). There were no reports of revision due to lysis, wear, or liner disassociation. Seven revisions required removal of the Pinnacle Cup. There were no reports of revision in the CoP group.

Furthermore, the data on Pinnacle have remained consistently positive in a number of clinical publications, national joint registries and independent studies, similar to the one referenced previously. In another recent paper from the Mayo Clinic, results were reported from a comparative study on 9,584 acetabular cups over a 21-year period using data from the Mayo Clinic joint registry.3 The authors reported patient outcomes in terms of hazard ratios (risk) for revision, loosening and wear. Mid-term results on 236 Pinnacle standard polyethylene and 854 Pinnacle cross-linked polyethylene hips showed, overall, higher survivorship for both cohorts out to 8 years of follow-up, compared to other designs introduced after 1990. There were no cases of revision due to aseptic loosening, wear or osteolysis. The Pinnacle cross-linked polyethylene had the lowest risk of revision of either the cup and/or liner for any reason as compared to all other acetabular options except a small cohort of Implex implants, although the differences were not significant. Significant differences may still emerge with longer follow-up.

The success of the Pinnacle Hip System, based on various clinical sources, mirrors my own clinical experience. Among the 3,000+ Pinnacle cups I have implanted, I have had to perform reoperations on only four cups. Three were a result of surgical error (my own), with either too much anteversion on the cup or placement that was too vertical, resulting in impingement on the acetabular liner or edge loading of the liner. Two of these patients had polyethylene liners and one patient had a metal liner. The fourth patient with a MoM articulation developed ALVAL, or aseptic lymphocytic vasculitis-associated lesion, that required revision to a polyethylene liner.

Although complete follow-up is unavailable for all of my patients, I am unaware of any in my series of 888 patients with Marathon who have been revised for osteolysis or wear. Furthermore, since I began using the Pinnacle Hip System in 2001, the results have been positive and the vast majority of my patients have experienced good function with few, if any, problems (Figure).






Figure: Radiograph showing press fit total hip arthroplasty with S-ROM stem and Pinnacle cup.




































The Pinnacle Hip System also offers a modular MoM insert that mates with the same shell. Although MoM bearings have fallen out of favor recently, I still use them in appropriate situations. I have had extremely good success with this modular MoM bearing. I have implanted more than 1,300 large diameter (36 mm or greater) Pinnacle MoM bearings in the last 10 years and have only revised two as a result of problems with the bearing. Approximately 85% of these bearings have been 36 mm in diameter with most of the remainder being 40 mm, and a small percentage being 44 mm. Pinnacle’s modular bearing design seems to function differently than the jumbo-head/one-piece acetabular designs that have been prone to higher failure rates as of late.4 This is a complex problem due to many different variables including shell stiffness and thickness, deformation of the shells during insertion, clearance of the bearing, and the sub-hemispherical design of different shells.

The performance advantage of the Pinnacle modular metal liner is a result of many factors—some not entirely understood. However, I believe that the stiffness of the modular metal liner, the resistance of this liner to deformation and the ability to maintain an appropriate clearance of the bearing, are some of the more important factors that have led to the success of the Pinnacle modular MoM articulation.

Finally, registry data from the United Kingdom reinforce Pinnacle’s solid record. The most recent report from the National Joint Registry for England and Wales (NJR) showed that the most common cementless cup was the Pinnacle, at 34% of the total market. The most commonly used uncemented combination—Pinnacle and the Corail Hip Stem (DePuy)—yielded a 5-year survivorship of 97.7%, in more than 40,000 patients.4

Surgical technique

For surgeons starting out with the Pinnacle Hip System, the learning curve is minimal, and the design of the shell and liner is such that positive head/neck ratios can be achieved, allowing for increased stability of the construct. I have used the posterior approach during my career and this approach has historically had a higher dislocation rate than the direct lateral or anterior approaches.5 However, my dislocation rate with Pinnacle is typically less than 1%, aided by the ability to use 36-mm diameter heads with desirable head/neck ratios, in the majority of my cases. In the past I tended to use as large a head as possible to assist in minimizing dislocation. Yet, recent literature suggests a benefit to be gained from a dislocation standpoint with increasing head size up to 36 mm in diameter.6 However, it is still comforting to see these large heads in situ given the jump distance to dislocate the head is quite large. Therefore, I still use as large a head as possible against polyethylene. Recently, I began using 36-mm heads, even with larger shells, when implanting MoM bearings. I have had such success with this size bearing over the past 10 years that I feel more comfortable with the 36-mm head versus the 40-mm, or even 44-mm heads, for which I do not have such long-term follow-up.

The surgical technique itself is, again, similar to other devices and easy for surgeons to master. The technique that I have used successfully in more than 3,000 implanted Pinnacle shells is to ream 1 mm less than the cup I plan to implant. I typically use a shell trial that is 2 mm smaller than the cup I will be implanting. This allows me to gauge the fit of the final shell without enlarging the acetabular cavity that I have just prepared. This provides me with a reproducible 1-mm press fit when the final shell is implanted. I have found this to provide excellent press fit of the shell in almost all cases. Using this technique I am able to place approximately 80% of shells without supplemental screw fixation."[R]egistry data from the United Kingdom reinforce Pinnacle's solid record."

— Kirk A. Kindsfater, MD

Surgeons preparing to use the Pinnacle Hip System need to be cognizant that all systems’ acetabular components are not sized similarly. For instance, if surgeons have been using a system in which the shell is oversized by 1 mm, they may be accustomed to reaming line-to-line before implanting their final shell. Pinnacle, in contrast, is true to its description and sizing information. The surgeon should know the true nominal diameter of the shell to be implanted to decide how much to under-ream prior to placement of the final shell. The technique I have described above has worked well in almost all of my cases with Pinnacle.

Surgical options

The Pinnacle Hip System offers three primary cup options that include a no-hole (100 series), a cluster-hole with three grouped screw holes (Sector) and a tri-spike cup (300 Series). Polyethylene liner options include standard offset, +4 lateralized, 10° face changing, lipped and constrained. For revision THA patients or atypical primary patients where the bone has been compromised, I tend to use the Pinnacle multi-hole or revision shell with Gription® porous coating (DePuy). This coating has a higher coefficient of friction than standard Porocoat® porous coating (DePuy), and has the potential to provide better initial fixation when the bone is compromised. The fixation surface of Gription maintains a 63% porous, 300-micron pore structure, and has demonstrated a coefficient of friction of 1.2 in lab testing. This represents an improvement over standard porous coating.7 In some patients I choose not to use a Gription shell, because its high friction can sometimes make it slightly more challenging to insert than a traditional Porocoat shell.

As one of its revision cup offerings, Pinnacle has a deep profile (DPx) option that is useful for revisions where a protrusio deformity is encountered or where lateralization of the center of rotation is required. The Pinnacle revision cup has a thicker shell that allows for additional fixation in the form of rim screws.

Preoperative planning and templating for Pinnacle is straightforward and similar to other devices. Radiographs help determine the size of components needed. If there is substantial bone loss or other factors that could complicate the procedure, then appropriate implants such as Gription porous-coated revision shells—standard or deep profile—can be used.

In my opinion, one of the key advantages of Pinnacle is its adaptability to my patients’ morphological requirements, especially in difficult or revision cases where many intraoperative options might be required. The Pinnacle Hip System can comfortably handle most situations that will be encountered.

Postoperatively, the initial fixation of the Pinnacle cup allows full weight-bearing for almost all patients. I typically allow my THA patients to reduce dependence on assistive devices as tolerated. Usually at 3 months postoperative I allow patients to return to normal activities without significant restriction.

Conclusion

The Pinnacle Hip System has proven to be an extremely reliable and successful option for THA with more than 10 years of clinical experience. To date there have been more than 1 million Pinnacle shells provided to patients worldwide, with extremely positive results. Both patients and surgeons can feel comfortable that the most appropriate option for each situation will be available within one system. Finally, the mid-term clinical results reported on this system should give surgeons confidence that survivorship of this implant will meet their expectations.

References

1. Kindsfater K, Barrett WP, Dowd JE, et al. 99.9% midterm survival of the pinnacle multi-liner acetabular cup in a prospective multi-center study. Poster #P077 presented at: AAOS Annual Meeting; February 14-18, 2007; San Diego.

2. Barrett W, Kindsfater K. Midterm Survival of the Pinnacle Multi-Liner Acetabular Cup in a Prospective Multi-Center Study. DePuy Internal Data. May 31, 2011.

3. Howard JL, Kremers HM, Loechler YA, et al. Comparative survival of uncemented acetabular components following primary total hip arthroplasty. J Bone Joint Surg Am. 2011;93:1597-1604.

4. National Joint Registry 8th Annual Report 2011. http://www.njrcentre.org.uk/NjrCentre/Portals/0/Documents/NJR%208th%20Annual%20Report%202011.pdf. Accessed October 26, 2011.

5. Kwon MS, Kuskowski M, Mulhall KJ, Macaulay W, Brown TE, Saleh KJ. Does surgical approach affect total hip arthroplasty dislocation rates? Clin Orthop Relat Res. 2006;447:34-38.

6. Dowd J, Kindsfater K, Barrett W, et al. Large femoral heads can help reduce risk of dislocation in total hip arthroplasty. J Arthroplasty; 2008;23:318.

7. DePuy documentation. Pinnacle Acetabular Cup Design Rationale. http://www.depuy.com/sites/default/files/products/files/EO-129.pdf.

Kirk A. Kindsfater, MD, is chief of the Department of Adult Reconstruction, Poudre Valley Hospital, and is in private practice at the Orthopaedic Center of the Rockies, Ft. Collins, Colo. Dr. Kindsfater is a paid consultant for DePuy Orthopaedics, Inc.