Fascial plane blocks as diagnostic keys to persistent pain after hip replacement: Sequential PENG and sacral ESP approach

Abstract

Persistent pain after total hip arthroplasty (THA) remains a diagnostic and therapeutic challenge, often related to extra-articular or neuropathic mechanisms rather than prosthetic failure. We report the case of a 70-year-old female with chronic suprainguinal, anterolateral thigh and gluteal pain who underwent right THA in 2023. Lumbar MRI performed before surgery showed L4–L5–S1 disc protrusions, initially considered incidental. Despite correct prosthesis positioning, postoperative pain persisted identically to preoperative symptoms. A pericapsular nerve group (PENG) block with ropivacaine 0.1% (20 ml) and methylprednisolone 40 mg provided near-complete anterior pain relief within 6 hours. Two weeks later, a sacral erector spinae plane block with ropivacaine 0.1% (20 ml) and methylprednisolone 20 mg, combined with a repeat PENG, achieved complete and lasting pain resolution. At 90-day follow-up, the patient remained pain-free. Thorough preoperative assessment, including diagnostic nerve blocks, may help prevent unnecessary arthroplasty in atypical hip pain.

Introduction

Chronic hip pain is a major cause of disability worldwide, most commonly due to osteoarthritis, trauma, or dysplasia. When conservative management fails, total hip arthroplasty (THA) is considered the gold standard for restoring function and relieving pain.[1] Although THA generally provides excellent outcomes, persistent pain has been reported in up to 23% of patients.[2]

Persistent or recurrent pain after THA may arise from prosthesis-related complications such as loosening or infection but also from nonarticular sources including iliopsoas impingement, trochanteric pain syndrome, and referred pain from the lumbar spine.[3] Central sensitization, neuropathic mechanisms, and psychological comorbidities are also recognized risk factors for chronic postsurgical pain (CPSP).[1,4]

Some patients continue to experience pain identical to that described preoperatively, raising concern for inappropriate surgical indication. Reports suggest that between 5% and 25% of THAs may be performed without fully appropriate criteria.[5,6] Diagnostic anesthetic injections have been investigated as predictive tools since a positive response to local anesthetic correlates with improved postoperative outcomes.[7,8]

Recently, fascial plane blocks such as the pericapsular nerve group (PENG) block and the sacral erector spinae plane (ESP) block have emerged as promising options for both perioperative and chronic hip pain.[9,10]

We report the case of a patient with persistent pain after THA, successfully managed with sequential PENG and sacral ESP blocks, which highlights the diagnostic role of regional anesthesia and raises the question of surgical appropriateness. Written informed consent was obtained for publication.

Case Presentation

A 70-year-old female presented with chronic right hip pain radiating suprainguinally to the anterolateral thigh and posteriorly to the gluteal region. The pain was deep, sometimes resembling abdominal colic. The patient had undergone left THA in 2022 with complete relief [Figure 1], but persistent pain on the right led to THA in January 2023. She was also followed by a psychologist for chronic pain management and coping strategies related to emotional distress and functional limitations.

Figure 1.

Pain distribution and anatomical rationale for the sequential fascial plane blocks. The patient’s pain involved the suprainguinal, anterolateral thigh, and posterior gluteal regions. The PENG block targeted the articular branches of the femoral, obturator, and accessory obturator nerves (left), while the sacral ESP block provided coverage of the dorsal sacral rami and branches of the sacral plexus (right)

Lumbar MRI obtained before the right THA showed disc protrusions at L4–L5–S1, interpreted as incidental findings. At 2 months postoperatively, the patient continued to report identical pain. The discomfort extended along the anterolateral thigh and posterior gluteal region. Several orthopedic evaluations confirmed correct prosthesis positioning with no loosening, infection, or mechanical issues. A colonoscopy performed due to colicky pain was negative.

On physical examination, the surgical scar appeared well healed, with no local inflammation. Passive hip motion was full and painless, excluding prosthetic or capsular involvement. Palpation over the greater trochanter and inguinal crease was negative, whereas deep pressure over the suprainguinal region and anterior superior iliac spine reproduced the typical pain radiating to the anterolateral thigh. Palpation over the gluteal and sacral areas elicited a dull neuropathic-like pain extending toward the buttock. Straight leg raising and FABER tests were negative. Mild hypoesthesia over the anterolateral thigh suggested involvement of branches of the lateral femoral cutaneous or femoral nerve. These findings supported a neuropathic, extra-articular pain origin and justified a diagnostic regional approach.

A right-sided PENG block was performed under ultrasound guidance with ropivacaine 0.1% (20 ml) and methylprednisolone 40 mg. Within 6 hours, the patient reported near-complete disappearance of suprainguinal and anterolateral pain, with lasting benefits [Figure 2a].

Figure 2.

(a) PENG block. AIIS, anterior inferior iliac spine; PT, psoas tendon; IPE, iliopectineal eminence; FN, femoral nerve; FA, femoral artery; FV, femoral vein. (b) Sacral ESP block. ESP, erector spinae muscle; S1: 1^st sacral vertebra, S2: 2^nd sacral vertebra; S3: 3^rd sacral vertebra; FS1: 1^st sacral foramina; FS2: 2^nd sacral foramina

Two weeks later, as posterior gluteal discomfort persisted, a sacral ESP block was performed with ropivacaine 0.1% (20 ml) and methylprednisolone 20 mg, combined with a repeat PENG using the same mixture [Figure 2b]. Again, within 6 hours, pain resolved completely.

At follow-up visits at 15, 30, 60, and 90 days, the patient remained pain-free, with full recovery of mobility and quality of life. No complications occurred.

Discussion

Persistent pain after THA affects up to one quarter of patients despite correctly positioned prostheses.[2] Etiologies include both prosthesis-related and extra-articular mechanisms. Recognizing the latter is essential to avoid misdiagnosis and unnecessary surgery.

In this case, the patient’s preoperative pain—suprainguinal, anterolateral, and gluteal—was atypical for osteoarthritis and persisted unchanged after THA, supporting an extra-articular neuropathic origin. Preoperative MRI showed L4–L5–S1 disc protrusions matching this distribution, consistent with hip–spine syndrome, where lumbar pathology mimics hip pain.[3] Although the patient was receiving psychological support for coping with chronic pain, the complete resolution of symptoms following targeted nerve blocks confirmed a predominantly neuropathic, rather than psychosomatic, mechanism.

Rationale for block selection

The anterior and anterolateral hip capsules are innervated by articular branches of the femoral, obturator, and accessory obturator nerves—territories targeted by the PENG block, which deposits anesthetic between the psoas tendon and pubic ramus, providing extensive coverage while sparing motor function.[9,10] The posterior hip and gluteal regions receive innervation from the sciatic, superior gluteal, and posterior sacral branches (L4–S3), reached by the sacral ESP block through longitudinal spread along the dorsal sacral fascia[9] [Figure 1].

This complementary coverage justified the sequential strategy: PENG relieved anterior pain, while sacral ESP resolved residual posterior discomfort. The rapid and selective analgesic response after both procedures acted as a functional diagnostic test, confirming that the prosthesis itself was not the source of pain but rather peripheral neural irritation. If the pain had been purely articular, the pattern of relief would not have followed such a distinct regional distribution. The rapid onset (≤6 hours) after both blocks further supports a peripheral nociceptive rather than centrally sensitized mechanism.

Diagnostic and prognostic implications

Diagnostic hip injections predict surgical outcomes with high accuracy.[7,8] In this case, the patient’s response to fascial plane blocks identified the extra-articular, neuropathic source previously misattributed to joint degeneration. Preoperative neuropathic features and sensitization are recognized predictors of poor surgical outcome.[4] Furthermore, inappropriate indications are reported in up to 13% of THAs, and 25–46% are considered uncertain.[5,6] Incorporating regional anesthetic tests into preoperative evaluation could refine patient selection and reduce such errors.

Therapeutic implications

Sequential fascial plane blocks provided both diagnosis and durable relief, revealing a mixed anterior and posterior neural origin. Beyond their analgesic role, fascial plane blocks can serve as reversible diagnostic tests, offering a low-risk method to identify extra-articular pain generators before proceeding with irreversible surgical interventions. Their dual diagnostic–therapeutic function may reduce CPSP by improving diagnostic precision and guiding targeted pain management.[9,10]

Conclusion

Persistent pain after THA may stem from misattributed neuropathic sources rather than prosthetic dysfunction. The patient’s atypical preoperative pain persisted after surgery but resolved completely with sequential PENG and sacral ESP blocks. This case underscores the diagnostic value of fascial plane blocks and the need for careful preoperative evaluation—particularly in patients with coexisting lumbar pathology—to avoid unnecessary arthroplasty.

Author contribution

LG and CA were responsible for the concept, date collection, search, reviewing results, manuscript editing and review oversight. IS and PS were responsible for review oversight. All authors have agreed both to be personally accountable for the author’s own contributions and to ensure that questions related to the accuracy or integrity of any part of the work, even ones in which the author was not personally involved, are appropriately investigated, resolved, and the resolution documented in the literature. All authors approved submission.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.