Minimally Invasive Hip Arthroplasty
R. Michael Meneghini and Mark W. Pagnano
• The risks and benefits of minimally invasive surgical approaches for total hip arthroplasty (THA) remain controversial.
• There is no single definition of “minimally invasive” THA, but the term has been used for approaches with a shorter skin incision and for approaches that spread rather than transect muscles.
• Most prospective, randomized trials have shown little long-term demonstrable benefit of “minimally invasive” THA approaches.
• Some studies of “minimally invasive” THA have suggested more rapid early functional recovery with certain minimally invasive methods.
• Some studies of “minimally invasive” THA have identified increased complication rates, especially early in the surgical learning curve.
Introduction and Background
Minimally invasive surgical (MIS) approaches to hip arthroplasty remain controversial and have gained the attention of patients and surgeons alike. Some investigators report that MIS techniques result in faster rehabilitation and rapid recovery after total hip arthroplasty (THA).1–8 However, an increased rate of complications has been reported with minimally invasive techniques,9–13 and significant learning curves have been associated with the various MIS surgical approaches.9,14,15 It has been reported that total hip replacements performed via MIS techniques may have a substantially higher early failure rate compared with THAs performed through a standard surgical approach.12
The exact meaning and definition of “minimally invasive” as it relates to surgical approaches in total hip arthroplasty remain ill defined. It has been reported that the skin incision size itself does not appear to affect early functional outcomes of total hip arthroplasty, with both the mini-posterior approach16 and the mini-direct lateral approach.17 More recently, the term “minimally invasive” is being used for approaches that claim to avoid muscle damage by performing THA through an internervous plane, such as the direct anterior approach, which avoids directly transecting or cutting muscles. This concept was originally popularized by proponents of the MIS two-incision approach. However, both direct anterior and two-incision procedures in THA have been shown to damage muscle,18,19 despite claims to the contrary.
This chapter will discuss available research and evidence surrounding various minimally invasive surgical approaches for total hip arthroplasty. It is beyond the scope of this chapter to discuss details of the various surgical approaches or surgical techniques. Rather, our intent is to present available evidence on clinical results, patient rehabilitation, and recovery outcomes and potential complications of MIS approaches. Comparative clinical studies, cadaveric studies, and gait analyses are presented to compare and contrast the relative merits and potential drawbacks of MIS surgical approaches for THA.
Minimally Invasive Surgical Approaches
The posterior, or posterolateral, surgical approach to total hip arthroplasty is one of the most commonly employed approaches for hip replacement. It provides the benefit of relative sparring of the abductors along with rapid recovery of gait with a minimal incidence of residual limp. A randomized, prospective study utilizing an MIS technique that minimizes soft tissue and muscle trauma during surgery reports that the mini-posterior approach results in improved early pain and early function after THA.20 The authors reported a shorter hospital stay, less postoperative pain in the hospital, and less reliance on an assist device in the mini-posterior group; however, no clinical difference in pain or function was noted between MIS and standard groups after hospital discharge.20 In a recent prospective cohort study, MIS and standard posterior approach THA were compared for recovery and muscle trauma postoperatively.21 Muscle-derived enzymes and pain and function scores were documented preoperatively and postoperatively. The MIS approach group exhibited significantly less loss of blood, less pain at rest, and a faster rate of recovery, but clinical chemistry values and other clinical parameters were comparable, and no difference could be discerned.21 Chimento and associates reported on 60 patients who underwent THA via MIS or standard surgical approaches.22 Authors reported less blood loss and fewer patients who limped at 6 weeks following the MIS posterior approach compared with those who underwent the traditional posterior approach. However, operative time, transfusion requirements, narcotic usage, length of hospital stay, achievement of rehabilitation milestones, cane usage, and complications were similar in the two groups, and no difference was reported between the groups at 1- and 2-year follow-up.22
Contrary to the reports just described, published reports fail to demonstrate any substantial advantage for an MIS posterior approach compared with a traditional posterior approach. In a scientifically rigorous study, Ogonda and associates reported on 219 THAs performed through an MIS (less than 10 cm) or traditional posterior approach.16 All patients and staff were blinded to the size of the incision for the duration of the hospital stay, and identical perioperative pain and physical therapy protocols were used to minimize confounding variables. No significant difference was detected with respect to postoperative hematocrit, blood transfusion requirements, pain scores, or analgesic use, and the authors found no difference in early walking ability or length of hospital stay, component placement, cement-mantle quality, or functional outcome scores at 6 weeks. The authors concluded that the MIS posterior approach offers no significant benefit in the early postoperative period compared with a standard incision.16
Further studies have corroborated these findings, demonstrating minimal benefit of the MIS posterior approach over the traditional approach. In a prospective comparative cohort study of 42 MIS posterior approach THAs of shorter incision length versus 42 traditional posterior THAs, the authors reported no difference in preoperative Harris hip score (HHS), estimated blood loss, or length of hospital stay (P > .05).23 Authors reported that those patients undergoing MIS THA in this study expressed considerable enthusiasm regarding the cosmetic appearance of the surgical incisions, and their postoperative HHS was slightly higher than that of group 2 (P = .042). The authors concluded that total hip arthroplasty through a smaller MIS incision offers no dramatic clinical benefit other than cosmetic appeal.23 In a study with similar conclusions, Woolson and colleagues reported a consecutive series of patients who underwent 135 consecutive THAs with MIS (less than 10 cm in incision length) and traditional posterior approaches.24 The authors found no significant difference between the groups with respect to average surgical time, intraoperative blood loss, in-hospital transfusion rate, length of hospital stay, or patients’ disposition after discharge. The mini-incision group was found to have a significantly higher risk of a wound complication (P = .02), a higher percentage of acetabular component malposition (P = .04), and poor fit and fill of femoral components inserted without cement (P = .0036).24 The authors concluded that no evidence was available to support the use of a small incision when THA is performed through a posterior approach.
Anterolateral (or Direct Lateral) Approach
The anterolateral (or direct lateral or modified Hardinge) approach is a long-standing and well-popularized surgical approach for total hip arthroplasty. The down-side of this approach is the inevitable muscle damage with occasional persistent limp that occurs secondary to splitting of the gluteus medius and minimus muscles; the benefit is the well-documented stability inherent in the approach because of preservation of the posterior capsule and short external rotators. In comparative studies, no conclusive evidence has suggested that an MIS anterolateral approach offers benefit in terms of recovery. A recent double-blind randomized controlled trial compared 120 consecutive primary uncemented THAs performed through MIS or through a traditional anterolateral or posterolateral approach.25 For patients in the MIS groups (average 7.8 cm incision length), minimally improved functional scores (HSS) were seen compared with the traditional approach groups at 6 weeks and 1 year, mainly caused by favorable results of the MIS posterior approach. In the MIS groups, surgical time was longer and a learning curve was observed based on operation time and complication rates. The authors also noted an excessively high perioperative complication rate in the anterolateral MIS group and concluded that MIS surgical approaches did not result in substantial benefit in the first postoperative year.25 In further support, a study of 60 THAs was undertaken to evaluate clinical advantages of performing THA through a single-incision, MIS (less than 10 cm) direct lateral approach compared with a standard-length skin incision.17 The authors failed to demonstrate any significant difference with regard to operative time, in-hospital opioid consumption, blood loss, complications, hospital length of stay, or functional scores at 6 weeks. They concluded that the MIS direct lateral approach does not appear to afford any clinical advantage to the patient in the short term and may create technical challenges that have the potential to adversely affect long-term outcome.17
Direct Anterior Approach
The direct anterior approach has been promoted as an intermuscular and internervous MIS approach to THA that provides the potential for early recovery and pain minimization as a result of decreased muscle damage. Analogous to the anterolateral approach, the direct anterior approach maintains inherent hip stability through relative avoidance of posterior structures, including the hip capsule. However, during the technically challenging aspect of the procedure, mobilization and exposure of the femur may necessitate release of the piriformis and the posterior capsule.19 Additional technical issues related to this approach include whether or not a specific (and frequently costly) operating table is required to perform the approach, the increased incidence of lateral femoral cutaneous nerve palsy,13 and the learning curve associated with minimizing complications.14,15 Regardless, the direct anterior approach is currently gaining interest and acceptance from surgeons and patients as a true MIS approach alike owing to claims of early recovery and return to function.
The direct anterior approach is currently gaining interest and acceptance from surgeons and patients alike as a true MIS approach. In a prospective, randomized trial comparing a single-incision modified Smith-Peterson approach versus a direct lateral approach, 100 patients were followed through the same perioperative protocol.26 No difference was demonstrated between the two groups in operative time, estimated blood loss, analgesia requirement, transfusions, or length of stay. The authors reported that up to 1-year follow-up, the direct anterior approach group demonstrated significantly better improvement in the mental and physical health dimensions of Short Form-36 and the Western Ontario McMaster Osteoarthritis Index compared with the direct lateral approach group; however, at 2 years, the results in these groups were the same.26 These early functional benefits have been supported with gait analysis. In a comparative report of 33 patients undergoing THA via a traditional anterolateral or MIS direct anterior approach, gait analysis was performed preoperatively and postoperatively.27 The authors reported that MIS direct anterior approach patients improved in a larger number of gait parameters than patients receiving the traditional anterolateral approach, and most improvements occurred between the 6- and 12-week follow-ups.27
In a recent prospective, comparative study of 57 patients treated with MIS THA through a direct anterior approach or a posterior approach, serum creatine kinase (CK) levels and inflammatory markers were measured preoperatively and postoperatively.28 The rise in the CK level in the posterior approach group was significantly higher than that in the anterior approach group postoperatively. The authors concluded that the anterior total hip arthroplasty approach caused significantly less muscle damage than was caused by the posterior surgical approach, as indicated by serum CK levels. However, the overall physiologic burden, as demonstrated by measurement of inflammation marker levels, appears to be similar between the anterior and posterior approaches.28