Recent advances in polyethylene and ceramic technologies has allowed us to use larger size heads without compromising the wear properties of a THR. One benefit of this change has been proposed to be a lower incidence of dislocation. This is a retrospective study looking at the effect of using large heads in our patient population.

We retrospectively evaluated the dislocation rate in 913 THR's performed using the same standardized surgical technique employed by a single team of surgeons at our institution between 1995 and 2015. Patients were assigned to two groups: small (28 mm and smaller) (SH), large diameter heads (36 mm and larger) (LH). The cup position was measured and plotted to determine its status according to the Lewinnek safe zone (15°±10° for anteversion, 40°±10° for inclination).

Sixteen of the 472 SH dislocated (3.4 percent) while 5 of the 441 LH group (1.1 percent) (P=0.04). In all of the LH patients that dislocated the cup position was in the safe range of Lewinnek. However, in the LH group only 65 percent of the cups were in the safe zone.

Using the same surgical approach by changing the head size to 36 mm and larger, we were able decrease the dislocation rate significantly. Errors of cup positioning according to Lewinnek became oblivious when using large heads compared to small heads. In our opinion, using large heads in total hip arthroplasty makes a difference in terms of dislocation.

Two-stage exchange revision is the gold standard in treating an infected total hip arthroplasty. The new emerging gold standard appears to be using an antibiotic impregnated spacer made from polymethylmeta-crylate (PMMA) bone cement between two stages. However, a consensus has not been reached on the antibiotic to use in the cement and its dose. Vancomycin an aminoglycoside is widely used for this purpose in the PMMA cement in doses such as 3 to 9 gr per 40 gr polymer powder. The purpose of this study was to see if Vancomycin is as effective in safer low doses of 1 gr per 40 gr polymer powder.Between 1997 and 2002, twenty-six patients were treated for an infected hip arthroplasty with a two-stage exchange arthroplasty using a Vancomycin impregnated polymethylmetacrylate (PMMA) bone cement spacer. During the first stage all prosthetic material was removed and after debridement, irrigation an articulating spacer was made from PMMA cement (Surgical Simplex, Howmedica, Rutherford, NJ, USA). One gram of Vancomycin HCl (Vancomycin, Eli Lilly, USA) powder was added to each 40 gr polymer powder prior to curing the cement. After the first stage parenteral antibiotics were administered for six weeks. When erythrocyte sedimentation rate and the CRP returned to a normal level, the patient underwent the second stage were a cementless prosthesis was inserted. Intra-operative cultures and frozen sections obtained during the second stage were negative in all patients indicating successful treatment of the infection. Mean follow up after the second stage was 36 (range 24 to 74) months. Two patients had a reinfection after four months. These two patients were infected with gram-negative micro-organisms. This gave us a 92 percent infection eradication rate at 3 years. None of the patients suffered from Vancomycin related side effects.In this study we used a lower dose (1 gr per 40 gr polymer powder) of Vancomycin in the PMMA spacer instead of the commonly used 3 to 9 gr per 40 gr polymer powder. The reason for this was our concerns for nephrotoxicity and allergic reactions frequently associated with use of Vancomycin. Antibiotics are used in cement spacers as a disinfecting agent and sterilizer of dead spaces. As Vancomycin is highly effective when used in PMMA due to its elution dynamics and thermostability we believed it would be effective even in low doses. In all patients the infection appeared to be cured after the first stage. This was demonstrated with negative intraoperative cultures and frozen sections. However, we had two reinfections in patients that initially were infected with gram-negative organism, which Vancomycin is not as effective. Despite this we were able to sterilize the infected hip with a low dose approach in the first stage. Vancomycin is effective in low dose when used in PMMA cement spacers for infected total hip arthroplasties. This approach will decrease potential serious side effects of Vancomycin.