Poster Exhibit October 2006 “Within Any Important Issue, There Are Always Aspects No One

Wishes To Discuss”- G. Orwell – Femoral Component Failure Keggi, K.1, Keggi, J.1, Kennon, R.1, Tkach, T.2, Low, W.2, Froehlich, J.3, McTighe, T.4, Cheal, E.5, Cipolletti, G.5

Introduction And Aims Reducing Fatigue Failure • Modular design allows for large Stem Removal Complications still occur in THA. One The most effective method of reducing selection of necks, to achieve Components are of these complications continues to be fatigue failure is to make improvements proper combination of designed with an femoral component failure. in design: lateral offset, leg length, and axial extraction anteversion This subject needs more open discussion. • Eliminate or reduce stress raisers by feature that The literature documents examples that streamlining the part; • Dual Press™ connection is facilitates simple, robust, and stable removal. This Retrieved stem. unsupported stems will fail regardless • Avoid sharp surface tears resulting from of fixation, material, and design but has • Indexing pin permits allows preservation of proximal bone punching, stamping, shearing, or other stock for re-implantation. not recently addressed the risk due to processes; selection of neutral, and 16º increased patient activity. anteversion position • Prevent the development of surface Apex Neck Retrievals Metal fatigue is caused discontinuities during processing; Dual Press™ by repeated cycling of the All retrieved stems that we have been load. It is a progressive • Reduce or eliminate tensile residual The Dual Press modular examined suggest quasi-static shear localized damage due to stresses caused by manufacturing; junction employs two failure of the alignment pin – a single • Improve the details of fabrication and areas of cylindrical high load (high torsion) event. There is no fluctuating stresses and Fatigue failure c.c. strains on the material. modular neck. fastening procedures. press-fit. evidence of fatigue failure as described Metal fatigue There are a number of methods available To create a mechanical lock, the proximal earlier. cracks initiate to a manufacturer to increase fatigue and distal diameters of the peg are and propagate strength and reduce fretting wear. slightly larger than the corresponding in regions However, no individual design, material, holes in the Apex’s Dual Press™ connection allows where the or process offers absolute guarantees stem, creating neck to fully seat. Stem provides medial strain is most with regard to mechanical failure given two bands of support, which Fractured titanium modular neck. increases strength and allows higher lateral severe. the increased popularity of high-impact interference, or offsets. The process of fatigue consists of three activities in todayʼs lifestyles. “press-fit”. stages: • Initial crack initiation Methods Results Kaplan-Meier survival analysis indicates a 98% survival at six years, • Progressive crack growth across the part including these mechanical failures. 1,568 cementless stems were implanted Twenty-two locking pins were sheared • Final sudden fracture of the remaining since June 2000 for primary THA resulting in torsional instability of the cross section featuring a proximal modular neck proximal modular junction. Patientʼs Apex Improvements design. All were implanted in six separate All devices are subject complaint of an initial popping sound Pin strength: to fatigue failure centers by eight surgeons. Twenty-two associated with a sense of hip instability Fractured chrome cobalt AML® femoral component failures (locking Old- 95 ft-lbs New- 216 ft-lbs especially with the monoblock stem. was consistent in all. Pain Plug increased patient activity we are seeing pins) occurred between 13 to 50 months was mild to moderate Bolt today. There are reports of device failure post-operatively. Each center used a with initial x-ray regardless of material, and different surgical approach (posterior, appearance normal. anterior muscle sparing, modified direct regardless of design style Surgical intervention Locating Pin Locating Pin (monoblock, modular). lateral) and a variety of cups and bearing surfaces. found locking pin to be Recent reports of failures sheared with rotational instability of Pin diameter has been Fractured titanium ® All cases were reviewed as to surgical Old New of modular revision stems SROM stem. the proximal neck and black staining of increased from .125” to have led to more vigorous technique; implant size, patient activity tissue due to metal debris. Twenty-one .188” along with added testing and the development of implants and examination of retrieved device. stems have been revised with standard feature of a bolt that with stronger modular junctions. In length cementless engages the stem. This addition stems have been designed with stems of a variety has resulted in +225% greater ability for bony fixation above the Material of designs. All increase in torsional strength. modular junction. It is anticipated that Apex Modular™ Stem Design have gone on to modular stems • Modular necks for optimized lateral full recovery. One Conclusions which allow for patient is not a fixation above offset, leg length, and anteversion Historical published reports on torsion surgical candidate loading along with BMI have been and below the • Key-hole proximal geometry with and is not experiencing any significant modular junction steps for good fill and initial stability underestimated. Increased patient pain. activities are subjecting devices to should be less Fx. c.c. cemented Fx. Bridge™ Titanium Fx. c.c. cementless • Circumferential plasma sprayed CP Cemented No material or fabrication defects were susceptible to late titanium coating unprecedented load levels. failure of those junctions. Recognizing found. No surgical errors were found. Current patient activities generate excess • Distal slot(s) for reduced end stem Mechanical testing demonstrated safety design and material limits is part of the stiffness of 95 ft pounds of torque. This review surgeonʼs responsibility in choosing the levels to be beyond published activity should be helpful in stem selection and appropriate implant. • No skirted heads loads. The culprit (in most cases) appears increased warning guidelines as to patient to be patient activity. activities.

2Joint Implant 4Keggi Surgery and Orthopaedic 3 University Orthopaedics, Research 5 Foundation, 2McBride Clinic, OKC, OK Omnilife Science, LLC., Inc., Providence, RI Foundation Waterbury, CT Raynham, MA