**6. Postoperative hip instability**

### **6.1 Hip precautions and does anterior hip need precautions**

Hip precautions have often been utilized to help aid in prevention of dislocation in the acute postoperative period. This is often done in patients who undergo a posterior approach where the short external rotators and the posterior capsule is compromised. Many physicians use these precautions. A recent prospective randomized trial from

Journal of Arthroplasty 2022 examined 346 consecutive patients all via posterior approach to the hip with a mean follow up of 2.3 years. This study demonstrated that if intraoperative hip stability was obtained at 90 degrees of flexion 45 degrees internal rotation and 0 degrees of abduction, postoperative hip precautions are no longer necessary. This study, however powerful, excluded patients with previous lumbar fusion, scoliosis or abductor insufficiency [149]. Mounts 2022 study is in accordance with another recently published a systematic review that included 6900 patients. This study demonstrated no statistically significant decrease in dislocations with the use of posterior hip precautions [150].

Since anteriorly based approachs are often regarded as a more stable approach post operatively, surgeons have questioned the need for precautions post operatively. Talbot et al. studied 499 cases of primary total hip arthroplasty done through an anterolateral approach and documented the dislocation rate when restrictions were not imposed. There were 3 early dislocations (within 6 weeks of surgery) all of which were close reduced, and every patient subsequently achieved a stable hip without further intervention [151]. Restrepo et al., also demonstrated a 0.16% dislocation rate which is significantly lower than the 2% overall that was found to occur within the 1st year by Maratt et al. in anterior and posterior approaches [34, 152]. The evidence for hip precautions after an anterior-based hip approach seems to be in favor of not requiring restrictions.

#### **6.2 Recognition of postop instability from infection, poly wear, ALTR**

To conclude, the surgeon must correctly identify the etiology of the instability to direct treatment. Early postoperative instability is likely due to component malpositioning or acute infection [116]. In cases of late stage instability the surgeon should consider component subsidence, aseptic loosening, osteolysis, indolent infection or the development of an adverse local tissue reaction (ALTR). Acute infection may be challenging to diagnose if obvious wound complications are not present [153, 154]. Both acute and chronic infection can present with loosening of one or both the acetabular and femoral components which may require staged revision. Another important cause of instability is aseptic loosening from polyethylene debris leading to macrophage induced osteolysis. This can ultimately lead to movement or dislodging of the implants which should be closely evaluated and may require revision surgery. Osteolysis can destroy available bone stock requiring the surgeon to become facile with bone grafting, cages, or even custom triflange implants for the acetabulum [155]. In the case of femoral bone loss there may be a need for diaphyseal engaging implants, bone grafting or even proximal femoral replacement [156]. Another potential cause of instability is the development of an ALTR from metal on metal (MOM) bearing surfaces. Diagnosis of ALTR is made from clinical history, radiography and serum metal ion levels. If surgery is deemed necessary, additional information may be obtained from ultrasound and metal artifact reduction sequence magnetic resonance imaging (MARS-MRI) to evaluate soft tissue destruction and possible need for augments or constraint due to abductor deficiency. Ultimately if serum ion levels continue to rise or patient functionality declines the patient will require revision surgery [157]. Although post-operative hip instability frequently requires revision surgery it is important to identify the root cause. This will allow the surgeon better surgical preparation, more readily available implants and the ability to manage infection with possible staged surgery or prolonged IV antibiotics.

*Instability in Total Hip Arthroplasty DOI: http://dx.doi.org/10.5772/intechopen.105801*
