The Viability of Short Stems in Total Hip Arthroplasty
Condition: Osteoarthritis of Hip
MeSH terms: Osteoarthritis, Hip
Study type: Interventional

Summary: 
      The purpose of this study is to determine the viability of short femoral stems as an
      alternative to standard-length stems in total hip arthroplasty.
    

Detailed description: 
      Porous-coated cementless stems were introduced in the late 1970s, in response to the high
      incidence of aseptic loosening associated with cemented stems (Judet et al 1978, Kavanagh et
      al 1989, Lord 1982, Stauffer 1982). The stem's porous surface achieves fixation via bony
      ingrowth at the endosteum (Engh et al 1987). In an effort to mimic the femur's natural stress
      distribution, many designs preferentially load the metaphysis (Joshi et al 2000). One such
      design is the proximally coated titanium tapered wedge, which is widely used today (Pitto et
      al 2010). Because loading is primarily dictated by bony ingrowth, the proximal porous coating
      avoids fixation at the diaphysis. The flat, tapered geometry reduces stiffness compared to
      cylindrical stems, thereby propagating stress to the proximal femur, rather than down the
      stem's axis (Engh et al 1987, Harvey et al 1999), (Boehm 1998). Further contributing to
      decreased stiffness is titanium's low elastic modulus, relative to that of cobalt-chromium
      (Harvey et al 1999, Mulliken et al 1996). Some contend the need for distal fixation in Dorr
      type C hips due to thin cortical bone at the metaphysis; however, proximally engaging stems
      have been shown to perform well in these patients (Kelly et al 2007, Reitman et al 2003).

      If a stem's objective is to load proximally, then perhaps it need not extend into the
      diaphyseal canal. The emergence of short stems has initiated an alternative means of proximal
      loading, without the disruption of diaphyseal bone stock. The smaller incisions involved with
      short stem total hip arthroplasty (THA) reduce damage to muscle and soft tissue (Molli et al
      2012). This enables a faster, more complete recovery for the patient, as well as a
      cosmetically superior result (Sherry et al 2003). Additionally, the preservation of
      bioavailable bone can be advantageous if a revision surgery is required (Toth et al 2010).
      Because short stems do not extend into the diaphysis, issues regarding proximal-distal
      mismatch of the femur are avoided (Patel et al 2013). This eases implantation and reduces the
      risk of intraoperative fracture (Azzam et al 2010, Cooper & Rodriguez 2010). The risk of
      intraoperative fracture is further mitigated because short stem THA does not require the use
      of reamers (Molli et al 2012, Scott et al 1975, Taylor et al 1978).

      Although the standard-length proximally coated titanium tapered wedge has a successful
      long-term track record, its design leaves room for improvement (Mallory et al 2001, Marshall
      et al 2004). Standard length stems cause stress-shielding in Gruen zones 1 and 7, suggesting
      that the diaphyseal portion of a stem may interfere with proximal loading (Gibbons et al
      2001, Schmidt et al 2004). Even proximally coated flat tapered stems are subject to
      diaphyseal loading (Cooper et al 2011). The Accolade stem has been associated with
      significant early subsidence, especially in males with Dorr type A hips (Jacobs & Christensen
      2009). This suggests that the stem may wedge distally, thereby interfering with
      osseointegration (White et al 2012). By achieving a purely metaphyseal fit, short stems can
      prevent excessive bone loss secondary to stress shielding (Gustke 2012). The investigators
      believe short stems are an equally effective alternative to traditional tapered stems in THA;
      however, long-term studies are essential to proving their efficacy.

      Long-term studies of short stems are lacking in current literature. With respect to initial
      stability and bony ingrowth, short-term data is promising; however, there is still potential
      for late aseptic failure (Capello et al 2009, Kroell et al 2009, Morales de Cano et al 2013,
      Schmidutz et al 2012). By conducting a single blinded, prospective, randomized investigation
      of two stems of varying length with equal metallurgy, coating, and proximal geometry, the
      investigators can identify the effects of stem length on long-term outcomes.
    

Intervention name(s): Taperloc standard length stem; Taperloc short length stem
Intervention type(s): Device; Device
Allocation: Randomized
Intervention model: Single Group Assignment
Masking: Single (Participant)
Primary purpose: Treatment