Introduction

Hip–spine syndrome (HSS) is characterized by the coexistence of hip osteoarthritis (HO) and lumbar degenerative disc disease. This condition was initially described and categorized by Offierski et al,1 who identified several subtypes: 1) simple HSS, where degenerative changes occur in both the hip and spine, but only one of these pathologies is the cause of disability; 2) complex HSS, with symptoms derived from both the hip and spine; 3) secondary HSS, where deformity in one location (hip or spine) exacerbates degenerative changes in the other location; and 4) misdiagnosed HSS, where symptoms from one location (hip or spine) mimic changes in the other location, leading to a wrong diagnosis. Both hip and spine disorders may manifest as pain radiating to the anterior thigh, buttock, knee, or even below, making differential diagnosis challenging in certain cases.2 The occurrence of both HO and lumbar spine disease (LSD) seems to be an increasing problem in the elderly population. Staibano et al3 reported that among 285 patients eligible for total hip arthroplasty (THA), 28.8% of those with end-stage HO experienced low back pain ranging from moderate to the worst imaginable.

This review provides a summary of current knowledge on HSS, with a focus on key aspects: 1) etiology, 2) differential diagnosis, 3) radiological parameters, 4) sequence and outcomes of surgical treatment.

Etiology of overlapping symptoms

The close anatomical relationship of the hip and lumbar spine often leads to overlapping symptoms of HO and degenerative LSD, complicating diagnosis when presentation is unclear. To understand this phenomenon, an overview of sensory innervation of the hip joint capsule may be helpful. The femoral nerve (L2–L4) supplies the anterior and anterolateral regions, the obturator nerve (L2–L4) supplies the anteromedial section, while the superior gluteal nerve (L4–S1), nerve to quadratus femoris (L4–S1), and sciatic nerve (L4-S1) innervate posterior areas.4 Specifically, the nerve to quadratus femoris targets the posteroinferior capsule, and the superior gluteal nerve covers the posterolateral capsule.4 Pathological changes occurring in either the hip or spine can influence the condition of the other region. Yukawa et al5 analyzed 512 patients diagnosed with lumbar disc herniation (L4/L5, L5/S1) without hip disease, of whom 21 (4.9%) reported groin pain. These patients were older, had more central disc herniation (often at the L4/L5 level), and rarely reported low back pain, as compared with the group without groin pain. The etiology of this pain was explained as the convergence of afferent fibers from the posterior annulus fibrosus or longitudinal ligament and the groin area on the same spinal cord neuron or associated cord interneurons.

Diagnosis

In some patients, distinguishing the symptoms of HO from those of spinal disorders can be difficult. Khan et al2 reported that groin and buttock pain were more prevalent among patients with HO, whereas calf pain was more common among individuals with spinal stenosis. However, there was no significant difference between the 2 groups regarding the presence of pain in other areas of the lower limb, such as the thigh, knee, and shin.2 Notably, 47% of the patients with HO experienced pain below the knee.2 Physical examination in conjunction with patient history-taking are crucial for making an accurate diagnosis. In this context, it is notable that only 15.8% of orthopedic trainees recognized that hip pain can radiate below the knee.2

In another study, 51 patients diagnosed with a hip joint pathology were asked to indicate painful places on an anatomic pain map.6 Overall, 71% of the patients reported pain referring to the buttock, while thigh and groin referral rates were 57% and 55%, respectively.6 None of these patients reported low back pain. The most common referral combination was buttock pain with thigh referral (20%).6 To distinguish these 2 conditions, it is essential to understand their typical presentations.

Lumbar spine–related symptoms

Radiculopathy may involve radiating pain and / or sensory loss along dermatomal territories. The pain can be described as burning, electric, dull, or aching.7 Some individuals with radiculopathy report low back pain, while others do not.8 Lumbar spine stenosis can manifest as bilateral buttock or leg pain that is alleviated by sitting or bending forward, and may be associated with a wide-based gait.9 Neurogenic claudication can also occur, often improving with anterior kyphotic flexion and sitting.9 Physical examination maneuvers applied to diagnose lumbosacral radiculopathy include manual muscle testing of ankle dorsiflexion and lateral toe extension,10 sensory testing,10 supine straight leg raise,11 Lasegue sign, and crossed Lasegue sign.12 Absent or reduced patellar tendon reflex suggests L4 radiculopathy, while decreased Achilles reflex points to L5/S1 involvement.13 Abnormal magnetic resonance imaging (MRI) findings are commonly observed in asymptomatic individuals.14 Therefore, MRI evaluation is advisable in patients with persistent symptoms to confirm the presence of radiculopathy prior to considering a surgical intervention.

Lumbar zygapophyseal joint arthropathy can also present as pain referred to the groin, hip, upper and lower lateral thigh, posterior thigh, or lateral aspect of the shin and foot.15 In this case, an analgesic response to facet joint injection or medial branch block is the only reliable and valid method to identify pain arising from the lumbar facet joints.15

Hip osteoarthritis–related symptoms

Among primary care patients with hip or groin pain, 34% had radiographic evidence of osteoarthritis.16,17 In the Framingham study (n = 946), only 15.6% of the hips with frequent pain showed radiographic evidence of osteoarthritis, while 20.7% of the hips with radiographically-confirmed osteoarthritis were often painful.18 The Osteoarthritis Initiative (a multicenter longitudinal cohort study of osteoarthritis in the United States; n = 4366) found that 9.1% of painful hips had radiographic evidence of osteoarthritis, and 23.8% of radiographic osteoarthritis–affected hips experienced frequent pain.19

A comprehensive diagnosis of HO requires correlating the patient’s symptoms, test results, and physical examination findings. Metcalfe et al20 reported the clinical findings most commonly associated with HO. The authors listed 3 findings from patient history that were linked to HO: a family history of HO (sensitivity, 34%; specificity, 84%; positive likelihood ratio [LR+], 2.1), a personal history of knee and hip osteoarthritis (sensitivity, 33%; specificity, 84%; LR+, 2.1), and pain when climbing stairs or walking down slopes (sensitivity, 68%; specificity, 68%; LR+, 2.1).20 The worst medial thigh pain had the highest LR+ (sensitivity, 12%; specificity, 98%; LR+, 7.8), but was rare (2.7% of the patients).20 Physical findings most strongly associated with HO included (in descending order): posterior hip pain during squatting (sensitivity, 24%; specificity, 96%; LR+, 6.1), groin pain on hip abduction or adduction (sensitivity, 33%; specificity, 94%; LR+, 5.7), abductor weakness (sensitivity, 44%; specificity, 90%; LR+, 4.5), decreased hip adduction (sensitivity, 80%; specificity, 81%; LR+, 4.2) and decreased internal rotation (sensitivity, 66%; specificity, 79%; LR+, 3.2) as measured by a goniometer or as compared with the contralateral leg.20 Normal passive hip adduction (sensitivity, 80%; specificity, 81%; negative likelihood ratio [LR–], 0.25) and abduction (sensitivity,88%; specificity, 46%; LR–, 0.26) were the most useful for excluding OA. Decreased range of motion was more indicative of OA than pain during movement alone.20

Differentiation

Rainville et al21 compared symptoms of 77 patients with HO and 79 individuals with lumbar spinal stenosis (LSS). They identified 8 symptoms more frequently associated with HO: groin pain (LR+, 4.9), knee pain (LR+, 2.2), pain that decreased with continued walking (LR+, 3.9), pain that occurred immediately with walking (LR+, 2.4), pain that occurred immediately with standing (LR+, 2.1), pain when getting in / out of a car (LR+, 3.3), pain when dressing the symptomatic leg (LR+, 3.1), and difficulty reaching the foot of the symptomatic leg while dressing (LR+, 2.3).21 Nearly all patients with HO (except for 2) exhibited at least 1 painful and restricted hip maneuver.21 Three symptoms were more commonly observed in the patients with LSS: pain below the knee (LR+, 2.3), leg tingling and / or numbness (LR+, 2.7), and some pain in both legs (LR+, 2.5).21 Nine percent of the patients with LSS demonstrated at least 1 painful or limited hip maneuver.21 Neurological deficits occurred in 39% of the patients with LSS, as compared with 20% of those with HO.21 Approximately half of the patients with HO experienced low back and buttock pain.21 Groin pain was most indicative of osteoarthritis, whereas leg tingling or numbness was most indicative of LSS.21

Intra-articular injection is a possible method for distinguishing pain induced by spinal disorders from pain caused by hip pathologies. A review by Maldonado et al22 showed that for intra-articular injection with an anesthetic alone, sensitivity for spine-related pain was 95.1%; specificity, 93.4%, positive predictive value, 97.2%; and negative predictive value, 78.1%. When using an anesthetic combined with corticosteroids, the mean values were: sensitivity, 93.1%; specificity, 95.3%; positive predictive value, 99.3%; and negative predictive value, 88.5%.22 However, this method is still not ideal and sometimes does not provide certainty regarding the origin of the pain.23

In HSS, a medical history, physical examination, and basic X-rays are usually sufficient to identify whether symptoms originate from the hip or spine. In more complex cases, identifying the source of pain can be difficult and may require further testing. When both hip and lumbar spine disorders are present and pain origin remains unclear, intra-articular hip injections guided by ultrasound or fluoroscopy can help establish a reliable diagnosis. Figure 1 illustrates the interaction between hip and spine pathology, as well as the symptoms characteristic of isolated hip osteoarthritis and lumbar spine disorders.

Figure 1. Hip–spine syndrome: interaction between hip and lumbar spine pathology with classification by Offierski et al.1 Hip pathology may lead to abnormal gait and compensatory overload of the lumbar spine, whereas lumbar spine pathology may result in abnormal posture and secondary hip symptoms.

Abbreviations: SLR, straight leg raise

Spinopelvic, postural, and hip radiologic parameters

Degenerative disease of the hip and spine affects posture and subsequently influences radiologic parameters (Figure 2). In individuals with spinal deformities and compensatory knee flexion, hip orientation is altered, displaying increased posterior and decreased anterior coverage, which together may restrict hip joint function.24 Piazzolla et al25 observed that patients with coexisting low back pain (LBP) and HO had significantly higher lumbar lordosis (LL), sacral slope (SS), pelvic incidence (PI), sagittal vertical axis (SVA), and a lower pelvic tilt (PT) than the patients with HO alone.

Figure 2. Spinal parameters assessed on radiographic images

Abbreviations: LL, lumbar lordosis; PI, pelvic incidence; PT, pelvic tilt; SS, sacral slope; SVA, sagittal vertical axis

Several studies reported alterations in spinal parameters following THA, which may explain the mechanism by which LBP improves after this procedure. Okuzu et al26 found that patients after THA with improved LBP showed maintained LL and PI–LL mismatch, as well as decreased SVA. Piazzolla et al25 observed that patients with concomitant LBP and HO who underwent THA presented a reduction in SS, LL, T1 pelvic angle, and SVA, as well as a significant increment of PT. The patients with unilateral HO and LBP had more anteverted femoral necks in the arthritic hip, as compared with the healthy side, a difference not seen in the HO patients without LBP.25 Liu et al27 found that individuals with improved LBP after THA had increased LL and decreased SVA, as compared with those with unimproved LBP; however, LL and SVA were reduced in both groups after surgery, albeit nonsignificantly. On the other hand, although Eyvazov et al28 reported improvements in LBP and static postural balance among patients with HSS after THA, they did not observe any significant changes in spinopelvic alignment postsurgery. Okuzu et al29 evaluated changes in spinal alignment after THA between patients with hyper LL and normal LL. They showed that the pelvis tilted more posteriorly, and there was a greater decrease in LL in the hyper LL group than in the control group after surgery.29 Pre- and postoperative Visual Analog Scale scores for LBP and clinical outcomes of THA were not significantly different between the groups.29 Muellner et al30 observed a marked improvement in spinal flexibility due to a decrease in sitting LL and an increase in standing LL among patients treated with THA. Simultaneously, disc height index increased significantly in each evaluated lumbar segment after the procedure.30 Improvement in hip flexion following THA was observed by Innmann et al.31 They noticed that the patients with HO who underwent THA, as compared with a group without HO, preoperatively demonstrated less mean change in hip flexion, greater mean change in PT, and greater mean lumbar movement when transitioning from a standing position to an upright-seated position.31 After THA, these parameters normalized, potentially eliminating abnormal mechanics that contribute to the development or exacerbation of HSS.31

Surgical treatment

Lumbar spinal fusion before total hip arthroplasty

Lavadi et al32 reviewed literature on surgical management of patients needing both hip and spine surgery, and found recent evidence that hip surgery should be prioritized. Previous lumbar spinal fusion (LSF) has been associated with poorer patient-reported outcomes,33,34 as well as an increased risk of hip dislocation33,35-37 and revision surgery following THA.33,37 The patients with a history of LSF who subsequently underwent THA showed higher rates of complications,38,39 reoperations, and general anesthesia within 90 days than those without prior LSF.38 Similarly, the patients who underwent THA before lumbar spine surgery had a lower risk of subsequent spinal surgery, opioid requirement, and postoperative hip dislocation, as compared with the individuals with an opposite surgical sequence.40 Additionally, the patients who underwent both THA and LSF demonstrated lower 8-year implant survival rates and a greater incidence of mechanical complications within the first 2 years, as compared with those who only underwent THA.41 Longitudinal data from the Humana Inc. database (n = 58 692) showed that 8.3% of the patients who underwent THA and spinopelvic fusion experienced dislocation, as compared with 2.9% of the patients with THA and no history of spinopelvic fusion.42 Zanirato et al37 conducted a systematic review comparing THA outcomes in patients with prior LSF, nonfused patients with stiff spine (non-SF Stiff), and nonfused patients with normal spine (non-SF), and reported dislocation rates of 5.98% for SF, 3% for non-SF Stiff, and 2.26% for non-SF, with significant differences between the groups. Dislocations were the primary reason for THA revision, and revision rates also differed significantly (7.3% for SF, 6.4% for non-SF Stiff, and 2.7% for non-SF; P = 0.02).37 On the other hand, Parilla et al43 found no difference in dislocation rates based on whether THA or LSF was performed first. However, the patients with LSF to the sacrum or those needing spinal revision had an increased risk of hip dislocation.43 The patients who experienced dislocation also showed lower LL, higher PT, and lower SS after LSF, as compared with those without dislocation.43 Enequvist et al44 found that patients who underwent LSF before THA reported better outcomes 1 year after the second procedure than those with an opposite order of interventions. The main improvement was observed for the patient-reported status prior to the second procedure and 1 year following this surgery, regardless of whether the second procedure was THA or LSF.44 These findings suggest that individuals with degenerative conditions affecting both the hip and lumbar spine may require surgical intervention at both sites to achieve improvements in health-related quality of life.44 Additionally, Pirkle et al45 found no association between prior LSF and long-term progression of osteoarthritis in native hips, as shown by no significant differences in the rate of THA between patients with and without prior LSF.

Total hip arthroplasty prior to lumbar spinal fusion

Performing THA first may confer greater benefit to patients by reducing the need for subsequent LSF, as shown by a low rate of LSF after initial THA (6%; 14 of 206). In contrast, 31 of 50 patients (62%) who underwent LSF required subsequent THA.46 Individuals with both severe HO and some degree of back pain after THA noted significant improvements in patient-reported outcome measures (PROMs), improvement in LBP, as well as better postural balance, with no significant changes in sagittal alignment.28,47 Ran et al48 reported LBP relief among 93.46% of the HSS patients following THA. Piazzolla et al49 found that clinical outcomes improved after THA in patients both with and without LBP, but more outcome measures reached significance in those with LBP. Chen et al50 tried to explain this phenomenon; they observed a significant decrease in an anterior tilt of the L4 and L5 lumbar vertebrae during gait after THA.50 This resulted in a more vertical orientation of the lumbar spine and decreased facet joint loading, which lead to improvement in LBP.50 The patients who undergo primary THA prior to lumbar spine surgery may experience reduced mobility, increased challenges in performing routine activities, and worse back pain following their spinal procedure, as compared with individuals without a history of hip surgery before a lumbar intervention.51 A prior total hip replacement did not affect health-related quality of life, leg pain, disability, or outcome satisfaction 1 year after lumbar spine surgery.51 Patients with coexisting LSD tend to show less improvement in hip function scores and health-related quality of life following THA than those without LSD.52 Higher preoperative Oswestry Disability Index score was associated with worse outcomes concerning the hip joint (Oxford Hip Scores, Harris Hip Scores) at 6 months and 1 year after hip replacement.3 Gong et al53 reviewed 6 retrospective studies to assess the effects of THA on complications and outcomes in patients treated with LSF. They found that THA performed more than 2 years before LSF was linked to fewer cases of adjacent segment disease (ASD), as compared with a lack of THA history.53 However, in the patients who underwent THA after LSF, the risk of ASD, pseudoarthrosis, revision LSF, and mechanical failure was higher than in those who underwent LSF without previous THA.53 The patients undergoing LSF within 2 years of THA had higher rates of deep vein thrombosis, neurological complications, prolonged opioid use, and revision LSF than those who underwent LSF without prior THA.53 No significant difference in revision LSF rate was observed when THA occurred over 2 years before LSF, while this rate was higher for the patients who underwent THA within 2 years prior to LSF, as compared with those who underwent LSF without a history of THA.53 Grammatopulos et al39 observed that patients who underwent THA prior to spinal arthrodesis demonstrated higher Oxford Hip Scores and Harris Hip Scores; however, there was no observable difference in PROMs or significant variation in spinopelvic parameters, complication rates, or revision rates based on the sequence of procedures. Fan et al54 demonstrated that both surgical sequences (THA first or LSF first) were associated with notable postoperative improvement in clinical function scores and radiologic parameters relative to preoperative values. No significant differences were observed between the groups in terms of functional outcomes or complication rates. Radiologic assessments showed that THA performed before LSF resulted in lower PT and higher SS, indicating more beneficial effects on pelvic alignment for this surgical sequence.54

A decision-making flowchart for patients presenting with overlapping hip and lumbar spine symptoms is presented in Figure 3.

Figure 3. Decision-making flowchart for patients presenting with overlapping hip and lumbar spine symptoms

Abbreviations: MRI, magnetic resonance imaging

Conclusions

Diagnosing HSS can be challenging; a comprehensive medical history taking and careful physical examination are crucial for reaching the correct diagnosis. Characteristic symptoms can support the diagnostic process, although considerable overlap between hip and spinal conditions may complicate differentiation. It is important to assess individuals with lower back pain for possible HO, and those with groin or hip pain for potential LSD. In complex cases, intra-articular anesthetic injections may be considered to facilitate differentiation. Meta-analyses evaluating the effect of surgical order showed that patients undergoing THA before LSF experience fewer complications, such as hip dislocation and revision procedures, and achieve better clinical outcomes. Additionally, many patients with low back pain experience symptom relief following THA.