In regard to the primary endpoint, this study has demonstrated that, whilst the prevalence of complications following THA was not statistically different amongst the three approaches, there was a higher overall rate of revision for the anterior approach, and this was due to early revisions for PPF.
The benefits and drawbacks of the different surgical approaches for THA continue to be a source of some debate and controversy. Studies supporting the use of the anterior approach have reported shorter lengths of inpatient stay, improved clinical and functional outcomes, improved gait dynamics and a lower dislocation rate [2, 3, 12, 13]. However, other studies report a higher risk of complications especially early after surgery .
The commonest complications following THA in our study were fractures. There were a significantly higher proportion of fractures that went on to receive revision in the anterior approach group. If the fractures were detected and fixed intra-operatively, there were no revisions but if they occurred intra-operatively and were not recognised, then there was a higher revision rate. This was the case despite the use of fluoroscopy for the anterior approach in almost all the cases.
The fractures in the anterior group occurred in the calcar, and involved cement-less tapered wedge femoral prostheses, which were most commonly used in the anterior approach. The study by De Geest’s group et al.  showed the fractures in their study involved a single stem design. The effect of stem designs in different approaches was investigated by Panichkul et al.  and a higher stem revision rate was found in the anterior approach group utilising a tapered wedge stem; aseptic loosening and peri-prosthetic fractures occurred in this group compared to none in the posterior and lateral approach groups.
It is not known if the increased risk of fractures in the anterior approach can be attributed more to the approach itself, or the limitations of the implants or instrumentation. It has been theorised that the supine positioning, with the usage of traction tables and manipulation of the lower limb for surgical exposure, may result in higher forces during elevation of the femur and broaching . These can possibly increase hoop stresses at the calcar and when combined with certain prostheses designs, result in calcar fractures. The use of a positioning table itself has been studied  and not found to be an independent risk factor for femoral fractures.
It is probable that factors such as the positioning of the patient and femur, amount of exposure and instrumentation, while individually not causal factors of statistical significance, combine to elevate the risk of iatrogenic fractures above that of the posterior and lateral approach. Meneghini et al. found that the greatest proportion of early femoral peri-prosthetic fractures or loosening occurred in the anterior approach. A multivariate analysis controlling for gender, age, BMI, laterality, bilateral versus unilateral procedure, bone quality and femoral stem type did not reveal any significant influence on femoral component loosening, which may indicate that a complex interplay of factors leads to a combined effect on the increased likelihood of such complications in the anterior approach.
Seven of the fractures in the anterior group (53.8% of the fractures in the anterior group) were not detected on intra-operative imaging. This did not occur in the lateral or posterior approaches. This is again similar to the findings of De Geest et al., where peri-prosthetic fractures were only detected post-operatively on checking radiographs or being readmitted from rehabilitation. Malek et al.  also encountered the same in their study which had a 2.6% rate of occult intra-operative peri-prosthetic femoral fracture in the anterior approach, which was not identified on intra-operative image intensifier screening. This may point to technical limitations in the imaging quality of intra-operative imaging. Intra-operative imaging is utilised to check cup positioning and limb length, and a subtle cortical crack may go unnoticed by the surgeon who focused on the former. Surgeons who encountered complications were interviewed and felt that an intra-operative crack may have occurred on stem insertion and therefore was not detected with imaging.
The two patients with early subsidence without fractures required revision with stems which were significantly larger than those initially inserted. In absence of fractures, this appears to indicate that the limitations of current instrumentation and surgical exposure may cause issues during broaching in this approach. It is postulated that the surgeons had difficulty inserting the broach directly down the intramedullary canal, causing an inadequate filling of the canal and thus incorrect sizing of the femoral components.
The posterior approach is known to have a slightly higher risk of dislocations, whilst the anterior and lateral approaches allow for preservation of the posterior soft tissue envelope. Dislocation rates reported in literature for the posterior approach range from 1 to 5% , whilst that of the anterior approach ranges from 0.61 to 1.5% [20, 21] and that of the lateral approach ranges from 0.4 to 0.55% [11, 22]. Of interest is Meneghini’s  finding in that, although the majority of revisions for instability occurred in the posterior approach (47.5%), the revision rate for instability in the anterior group was 37.5%. Other studies involving matched cohorts and a registry report of 11,112 matched registry cases revealed no difference in dislocation rates between the anterior approach and posterior approach [23, 24], with the authors concluding that the posterior approach, with capsular repair, and the use of larger femoral heads, has decreased the risk of dislocation to a level comparable to that of the anterior approach.
The rate of dislocation in our study parallels that in literature, with the rates for anterior, lateral and posterior approaches being 0.5, 0.2 and 0.9% respectively. Revision rates due to dislocations did not differ significantly across the 3 approaches. Again, whilst the numbers are small, the heterogeneity of the study population does indicate that in the real world setting, the risk of dislocation is not completely removed by the anterior approach, and attention on the surgeon’s part with respect to acetabular cup and femoral stem positioning is still paramount, regardless of approach. As with fracture complications, neither gender nor BMI appeared to be risk factors for instability.
SSIs and haematomas
The anterior approach has been linked to an increased re-operation rate due to wound complications, such as haematomas with or without infection, delayed wound healing or prosthetic joint infections . This has been attributed to the thinner skin in the proximal thigh as compared to the lateral thigh, the proximity to the waist crease and the increased skin tension across the flexion crease causing raised shear stresses .
A study by Jahng  has looked into risk factors for wound complications after THA by an anterior approach. Their findings were that a BMI of > 30 kg/m2 and diabetes placed patients at greater risk for wound complications and re-operation. This may serve as a guide to surgeons when considering the suitability of patients for the anterior approach.
In our patients, only 4 out of 12 patients had BMI > 30 kg/m2 but the low numbers did not allow us to analyse if BMI was a risk factor for wound complications. Among the patients in which re-operation was required for SSI, there did not appear to be any approach associated with an increased risk of SSI. In addition, whilst half of the patients with SSIs went on to require revision of implants, there was no significant difference in revision rate for infection among approaches.
Venous thromboembolic events
There has been no recent literature comparing the rates of venous thromboembolic events (VTE) among the approaches and in our patients, VTE occur in the different approaches. Five out of 7 of the patients who had VTE were female. In our patients, whist BMI was more than 30 kg/m2 for 4 patients out of 7, with an average of 31.6 kg/m2. However, the numbers are too low to allow analysis if gender or BMI are significant risk factors. Thus the incidence of VTE in patients undergoing THA in our institution appears to be a function of known risk factors as established in literature as opposed to being approach specific.
There are several strengths to this study. It examines the overall complications of all THA performed at a large tertiary hospital group and includes the results of all the surgeons performing arthroplasty, and not just from a specialized joint arthroplasty centre. All procedures were linked to the AOA NJRR to capture all revisions including those that may not have occurred at the hospital. A case record review was performed of all complications as distinct from relying on information from an administrative dataset review. There are also limitations to this study. Although data are collected on length of time of surgery the setup for the anterior hip approach with a traction table and fluoroscopy is recorded within the whole theatre time. Therefore this may have lengthened the time of the operation recorded for the anterior approach compared to that for patients receiving the lateral or posterior approaches. Because of this we were unable to directly examine whether length of surgery is correlated with complications. We also did not analyse the data by surgeon experience and are aware of the effect of the learning curve on the rate of revision for the anterior approach to the hip . However, the study period was well after the introduction of the anterior approach and the majority of surgeons in the group were experienced in anterior approach to the hip. Finally, data regarding femoral head sizes were not consistently recorded for all patients and analysed in this study with regards to dislocation rates across the 3 surgical approaches.