Motor nerve palsy following primary total hip arthroplasty

Femoral Nerve Palsy Following Total Hip Arthroplasty: Incidence and Course of Recovery

BACKGROUND

Femoral nerve palsy (FNP) is a relatively uncommon complication following total hip arthroplasty (THA). There is little recent literature regarding the incidence of FNP and the natural course of recovery.

METHODS

Using our institutional database, we identified postoperative FNPs from 17,350 consecutive primary THAs performed from 2011 to 2016. Hip exposures were performed using a direct lateral (modified Hardinge), direct anterior (Smith-Peterson), anterolateral (Watson-Jones), or posterolateral (Southern or Moore) approach. Patients with FNP were contacted to provide a subjective assessment of convalescence and underwent objective muscle testing to determine the extent of motor recovery.

RESULTS

The overall incidence of FNP was 0.21% after THA, with the incidence 14.8-fold higher in patients undergoing anterior hip surgery using either a direct anterior (0.40%) or anterolateral (0.64%) approach. Significant recovery from FNP did not commence for a majority of patients until greater than 6 months postoperatively. Motor weakness had resolved in 75% of patients at 33.3 months, with remaining patients suffering from mild residual weakness that typically did not necessitate an assistive walking device or a knee brace. Nearly all patients had improved sensory manifestations, but such symptoms had completely resolved in less than 20% of patients.

CONCLUSION

FNP after hip surgery remains relatively uncommon, but may increase with a growing interest in anterior THA exposures. A near complete recovery with only mild motor deficits can be expected for a majority of patients in less than 2 years, although sensory symptoms may persist.

Changing practice for hip arthroplasty and its implications

This overview provides insight into changes in clinical practice and the implications for nursing staff and clinicians who are involved in the management of patients undergoing primary total hip arthroplasty. The review highlights commonly used surgical approaches, their advantages, their associated risks and how to manage complications if they occur.

Nerve injuries associated with total hip arthroplasty

Nerve injury is a relatively rare, yet potentially devastating complication of total hip arthroplasty (THA). Incidence of this ranges from 0.6 to 3.7%, and is highest in patients with developmental hip dysplasia and previous hip surgery. Apart from patient and surgeon dissatisfaction, this complication can have medico-legal consequences. Therefore, the purpose of this study was to review the risk factors, etiology, diagnostic options, management strategies, prognosis, and prevention measures of nerve injuries associated with THA. We specifically evaluated the: 1) sciatic nerve; 2) femoral nerve; 3) obturator nerve; 4) superior gluteal nerve; and 5) the lateral femoral cutaneous nerve.

Magnetic resonance imaging patterns of mononeuropathic denervation in muscles with dual innervation

Magnetic resonance imaging (MRI) of mononeuropathy in muscles with dual innervation depicts geographic denervation corresponding to the affected nerve. Knowledge of the normal distribution of a muscle's neural supply is clinically relevant as partial muscle denervation represents a potential imaging pitfall that can be confused with other pathology, such as muscle strain. This article reviews the normal innervation pattern of extremity muscles with dual supply, providing illustrative examples of mononeuropathy affecting such muscles.

Sciatic Nerve Palsy following Total Hip Replacement: Are Patients Personal Characteristics More Important than Limb Lengthening? A Systematic Review

Sciatic nerve palsies are rare but potentially devastating complications, accounting for more than 90% of neurologic injuries following total hip replacement. A systematic literature screening was carried out searching papers evaluating an exclusive population of postarthroplasty sciatic nerve palsies to ascertain (1) the influence of limb lengthening itself on sciatic nerve palsy, (2) the most important risk factors, (3) the long-term prognosis, and (4) the outcomes of different treatments. Fourteen manuscripts were finally included. The wide prevalence of retrospective case series decreased the global methodological quality of the retrieved papers. A hazardous lengthening threshold cannot be surely identified. Developmental dysplasia of the hip and previous hip surgeries are the most frequently recognized risk factors. Rate of full nerve function restoration approximates two-thirds of the cases, independently of the extent of initial neural damage. Poor evidences are available about the best treatment strategy. Well-structured multicentric prospective comparative studies are needed to substantiate or contrast the finding of this review. Anyway, since the onset of palsies is probably due to a combination of individual factors, risk of nerve damage and potential for nerve recovery should be evaluated on an individual basis.

Systematic review of the outcome of total hip arthroplasty in patients with sequelae of Legg-Calvé-Perthes disease

BACKGROUND

Total hip arthroplasty (THA) in patients with sequelae of Legg-Calvé-Perthes disease (LCP) is technically demanding because of the disease related deformities occuring in the proximal femur and/or the multiplanar deformities secondary to corrective osteotomies in childhood. Little is known about the long-term outcome of the procedure in this challenging group of patients.

METHODS

We carried out a systematic review of the literature to determine the functional outcome, complications and revision rate of THA in patients with sequelae of LCP disease. Six out of 148 potential studies involving 245 hips met the inclusion criteria. The mean age was 45.7 years (19-74) and follow-up was 8.4 years (2-21).

RESULTS

There were 221 cementless THAs (90%), 22 hybrid THAs (9%) and 2 cemented THAs (1%). The femoral components used included 187 standard stems (76%), 43 modular stems (18%) and 15 custom-made stems (6%). The modular implants used were reamed S-Rom stems. All studies reported a significant improvement in hip function following THA. There were 16 revision THAs (7%) occurring at a mean of 7.5 years (0.4-10.3). Complications included intra-operative fracture (11%, n = 27), aseptic loosening (5%, n = 13), sciatic nerve palsy (3%, n = 7) and heterotopic ossification (2%, n = 4). All intra-operative fractures occurred when standard femoral stems were used. The average limb lengthening in the patients with a post-operative sciatic nerve injury was 1.9 cm. All patients with this complication had a history of previous hip surgery.

CONCLUSIONS

THA in patients with LCP disease results in similar functional outcome compared to patients with primary osteoarthritis; however, the revision rate at mid-term follow-up is slightly increased. Reamed modular (S-Rom) and custom femoral implants appear to be associated with a decreased risk of intra-operative fracture. Care should be taken when addressing leg length discrepancy in this group of patients due to the increased risk of sciatic nerve palsy, especially in patients with prior surgical procedures.

High-resolution metal artifact reduction MR imaging of the lumbosacral plexus in patients with metallic implants

OBJECTIVE

To assess the quality and accuracy of metal artifact reduction sequence (MARS) magnetic resonance imaging (MRI) for the diagnosis of lumbosacral neuropathies in patients with metallic implants in the pelvis.

MATERIALS AND METHODS

Twenty-two subjects with lumbosacral neuropathy following pelvic instrumentation underwent 1.5-T MARS MRI including optimized axial intermediate-weighted and STIR turbo spin echo sequences extending from L5 to the ischial tuberosity. Two readers graded the visibility of the lumbosacral trunk, sciatic, femoral, lateral femoral cutaneous, and obturator nerves and the nerve signal intensity of nerve, architecture, caliber, course, continuity, and skeletal muscle denervation. Clinical examination and electrodiagnostic studies were used as the standard of reference. Descriptive, agreement, and diagnostic performance statistics were applied.

RESULTS

Lumbosacral plexus visibility on MARS MRI was good (4) or very good (3) in 92% of cases with 81% exact agreement and a Kendall's W coefficient of 0.811. The obturator nerve at the obturator foramen and the sciatic nerve posterior to the acetabulum had the lowest visibility, with good or very good ratings in only 61% and 77% of cases respectively. The reader agreement for nerve abnormalities on MARS MRI was excellent, ranging from 95.5 to 100%. MARS MRI achieved a sensitivity of 86%, specificity of 67%, positive predictive value of 95%, and negative predictive value of 40%, and accuracy of 83% for the detection of neuropathy.

CONCLUSION

MARS MRI yields high image quality and diagnostic accuracy for the assessment of lumbosacral neuropathies in patients with metallic implants of the pelvis and hips.

Nerve Decompression Surgery After Total Hip Arthroplasty: What Are the Outcomes?

BACKGROUND

The purpose of our study was to compare (1) muscle strength; (2) pain; (3) sensation; (4) various outcome measurement scales between post-total hip arthroplasty (THA) patients who had a sciatic nerve injury and did or did not receive decompression surgery for this condition; and (5) to compare these findings with current literature.

METHODS

Nineteen patients who had nerve injury after THA were reviewed. Patients were stratified into those who had a nerve decompression (n = 12), and those who had not (n = 7). Motor strength was evaluated using the Muscle Strength Testing Scale. Pain was evaluated by using the visual analogue scale. Systematic literature search was performed to compare the findings of this study with others currently published.

RESULTS

The decompression group had a significant improvement in motor strength and the visual analog scale scores as compared with nonoperative group. Patients in decompression group had a significant larger increase in the mean Harris hip score and University of California Los Angeles score. There was no significant difference in the increase of Short Form-36 physical and mental scores between the 2 groups. Literature review for nonoperative management yielded 5 studies (93 patients), with 33% improvement. There were 7 studies (81 patients) on nerve decompression surgery, with 75% improvement.

CONCLUSION

This study demonstrates the benefits of nerve decompression surgery in patients who had sciatic nerve injury after THA, as evidenced by results of standardized outcome measurement scales. It is possible to achieve improvements in terms of strength, pain, and clinical outcomes. Comparative studies with larger cohorts are needed to fully assess the best candidates for this procedure.

Position of the sciatic nerve and effect of gluteus maximus release during hip arthroplasty

Eight Thiel embalmed hips were dissected. The distance between the sciatic nerve and the femoral neck was measured before and after hip dislocation, and before and after release of the gluteus maximus tendon. There was a significant reduction in the mean distance between the neck of femur and the sciatic nerve in both the gluteus maximus tendon release and the unreleased groups at 60° and 90° of hip flexion, p < 0.05. The mean distance between the neck of femur and sciatic nerve was greater in the release group for all positions.

Post-operative neuropathy after total hip arthroplasty

Nerve palsy is a well-described complication following total hip arthroplasty, but is highly distressing and disabling. A nerve palsy may cause difficulty with the post-operative rehabilitation, and overall mobility of the patient. Nerve palsy may result from compression and tension to the affected nerve(s) during the course of the operation via surgical manipulation and retractor placement, tension from limb lengthening or compression from post-operative hematoma. In the literature, hip dysplasia, lengthening of the leg, the use of an uncemented femoral component, and female gender are associated with a greater risk of nerve palsy. We examined our experience at a high-volume, tertiary care referral centre, and found an overall incidence of 0.3% out of 39 056 primary hip arthroplasties. Risk factors found to be associated with the incidence of nerve palsy at our institution included the presence of spinal stenosis or lumbar disc disease, age younger than 50, and smoking. If a nerve palsy is diagnosed, imaging is mandatory and surgical evacuation or compressive haematomas may be beneficial. As palsies are slow to recover, supportive care such as bracing, therapy, and reassurance are the mainstays of treatment. Cite this article: Bone Joint J 2017;99-B(1 Supple A):46-9.

Surgical Approaches for Total Hip Arthroplasty

Total hip arthroplasty (THA) has become one of the most reliable and patient-requested surgical interventions in all medicine. The procedure can be performed using a variety of surgical approaches, but the posterior approach, direct lateral approach, and direct anterior approach are by far the most common across the globe. This article highlights the history and technique for each of these common approaches. A review of outcomes and complications for each approach are also provided. Each approach has its own unique advantages and disadvantages, but all can be safely and successful utilized for THA. Strong, convincing, high-quality studies comparing the different approaches are lacking at this time. Surgeons are therefore recommended to choose whichever approach they are most comfortable and experienced using. Though not described here, THA can also be done using the anterolateral approach (also known as the Watson Jones approach) as well as the two-incision approach. In addition, recently, some surgeons are utilizing the so-called direct superior approach for THA. While these approaches are far less commonly utilized, they are recognized as viable alternatives to traditional approaches.

Nerve Palsy after Total Hip Arthroplasty without Subtrochanteric Femoral Shortening Osteotomy for a Completely Dislocated Hip Joint

Background:

Neurological injuries are a rare but devastating complication after total hip arthroplasty (THA). The purpose of this study was to retrospectively determine the frequency of nerve palsy after THA without subtrochanteric femoral shortening osteotomy in patients with a completely dislocated hip joint without pseudo-articulation between the femoral head and iliac bone.

Methods:

Between October 1999 and September 2001, nine primary THAs were performed for patients with a completely dislocated hip joint. The limb lengths, neurological abnormalities, and the extent of their neurological recovery were evaluated. Three THAs were combined with subtrochanteric femoral shortening osteotomy, and six THAs were combined without subtrochanteric femoral shortening osteotomy.

Results:

The mean length of the operation was 4.8 cm (range, 3.0-6.5 cm). Sciatic nerve palsy developed in four of the nine patients after THA. None of the cases with sciatic nerve palsy were combined with subtrochanteric femoral shortening osteotomy. Three of four patients did not completely recover from sciatic nerve palsy.

Conclusions:

THA for patients with a completely dislocated hip was associated with a high risk of nerve palsy due to excessive limb lengthening; the potential for recovery from nerve palsy was observed to be poor. Subtrochanteric femoral shortening osteotomy should be used in combination with THA in patients with a completely dislocated hip.

Delayed Femoral Nerve Palsy Associated with Iliopsoas Hematoma after Primary Total Hip Arthroplasty

Femoral nerve neuropathy after total hip arthroplasty is rare but catastrophic complication. Pain and quadriceps muscle weakness caused by this complication can significantly affect the functional outcome. Here we present a case report, describing delayed onset femoral nerve palsy associated with iliopsoas hematoma following pseudoaneurysm of a branch of profunda femoris artery after 3 months of primary total hip arthroplasty in an 80-year-old female patient with single kidney. Hip arthroplasty was done for painful primary osteoarthritis of left hip. Diagnosis of femoral nerve palsy was made by clinical examination and computed tomography imaging of pelvis. Patient was managed by surgical evacuation of hematoma and physiotherapy. The patient's clinical symptoms were improved after surgical evacuation of hematoma. This is the first case report of its kind in English literature regarding delayed onset femoral nerve palsy after primary total hip arthroplasty due to pseudoaneurysm of a branch of profunda femoris artery without any obvious precipitating factor.

No Difference in Dislocation Seen in Anterior Vs Posterior Approach Total Hip Arthroplasty

BACKGROUND

The direct anterior approach (DAA) for total hip arthroplasty (THA) has rapidly become popular, but there is little consensus regarding the risks and benefits of this approach in comparison with a modern posterior approach (PA).

METHODS

A total of 2147 patients who underwent DAA THA were propensity score matched with patients undergoing PA THA on the basis of age, gender, body mass index, and American Society of Anesthesia classification using data from a state joint replacement registry. Mean age of the matched cohort was 64.8 years, mean body mass index was 29.1 kg/m(2), and 53% were female. Multilevel logistic regression models using generalized estimating equations to control for grouping at the hospital level were used to identify differences in various outcomes.

RESULTS

There was no difference in the dislocation rate between patients undergoing DAA (0.84%) and PA (0.79%) THA. Trends indicating a slightly longer length of stay with the PA and a slightly greater risk of fracture, increased blood loss, and hematoma with the DAA are consistent with previous studies.

CONCLUSION

On the basis of short-term outcome and complication data, neither approach has a compelling advantage over each other, including no difference in the dislocation risk.

Does the combination of erythropoietin and tapered oral corticosteroids improve recovery following iatrogenic nerve injury?

INTRODUCTION

The reported prognosis for recovery after peripheral nerve injury is remarkably poor. Deficits may persist for years, resulting in significant functional disability. Both corticosteroids and Erythropoietin have been investigated as neuroprotective agents; however, their efficacy in total hip and knee arthroplasty is not known. The purpose of this study was to evaluate the effect of systemically-administered Erythropoietin and tapered oral corticosteroids on the recovery of postoperative nerve palsies in the setting of total hip and knee arthroplasty.

METHODS

Eleven patients sustaining postoperative peripheral nerve injuries after total hip or knee arthroplasty were treated acutely with Erythropoietin and tapered oral steroids. Motor and sensory function was assessed clinically pre- and postoperatively until complete motor recovery or for a minimum of 1 year.

RESULTS

Motor loss was complete in seven (64%) patients and partial in four (36%). Seven (64%) patients' symptoms affected the common peroneal nerve distribution and four (36%) had concomitant tibial nerve involvement. Eight (73%) patients experienced full motor recovery at an average of 39 days (range: 3-133 days), and three (27%) had near-complete motor recovery. At final follow up, no patient required assistive devices for ambulation.

CONCLUSIONS

Administration of Erythropoietin coupled with oral tapered steroids for patients sustaining iatrogenic nerve injuries in total hip and knee arthroplasty demonstrated faster and more complete recovery of motor and sensory function compared to previous reports in the literature. This study highlights the importance of further investigation to define the role of each in the setting of acute postoperative nerve palsies.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Foot drop following closed reduction of a total hip replacement

Sciatic nerve palsy has been well documented and reported, following primary and revision hip replacement. It can also occur following dislocation of hip replacement. The incidence of sciatic nerve palsy in dislocated hip replacement is <0.1%. However, new onset sciatic nerve palsy following a closed reduction of dislocated hip replacement is even rarer. We describe a case of sciatic nerve palsy from traction injury following closed reduction of a total hip replacement.

Distances between bony landmarks and adjacent nerves: anatomical factors that may influence retractor placement in total hip replacement surgery

Background

Retractor placement is a leading cause of intraoperative nerve injury during total hip replacement (THR) surgery. The sciatic nerve, femoral nerve, and superior gluteal nerve are most commonly affected. This study aimed to identify the distances from bony landmarks in the hip to the adjacent nerves on magnetic resonance imaging (MRI) and the associations between anatomical factors and these distances that would guide the placement of retractors during THR surgery, in order to minimize the risk of nerve injury.

Methods

We reviewed hip MRIs of 263 adults and recorded the distances from (1) the anterior acetabular rim to the femoral nerve; (2) the superior acetabular rim to the superior gluteal nerve; (3) the posterior acetabular rim to the sciatic nerve; and (4) the greater trochanter to the sciatic nerve. The effects of anatomical factors (i.e., gender, age, body height, body mass index (BMI), pelvic width, and acetabular version and morphology) on these distances were analyzed.

Results

Distances from bony landmarks to adjacent nerves (in cm) were 2.06 ± 0.44, 2.23 ± 0.28, 1.94 ± 0.81, and 4.83 ± 0.26 for the anterior acetabular rim, superior acetabular rim, posterior acetabular rim, and greater trochanter, respectively, and were shorter in women than in men (P < 0.001). Multivariate analysis identified body height as the most influential factor (P < 0.001). Linear regression demonstrated a strong positive linear correlation between body height and these distances (Pearson’s r = 0.808, 0.823, 0.818, and 0.792, respectively (P < 0.001)).

Conclusions

The distances from bony landmarks to adjacent nerves provide useful information for placing retractors without causing nerve injury during THR surgery. Shorter patients will have shorter distances from bony landmarks to adjacent nerves, prompting more careful placement of retractors.

Total hip arthroplasty with subtrochanteric femoral shortening osteotomy for high hip dislocation

OBJECTIVE

To evaluate the outcomes of total hip arthroplasty (THA) with subtrochanteric femoral shortening osteotomy for high hip dislocation.

METHODS

In this retrospective study, the results of 24 primary THAs with acetabular reconstruction and subtrochanteric femoral shortening osteotomy in 21 patients with high hip dislocation were evaluated. The acetabula were reconstructed with cemented or uncemented cups and bone grafting. Transverse subtrochanteric femoral shortening osteotomies were applied and the osteotomy sites treated by bone grafting and cable fixation. Assessment was by Hip Harris scores and radiographic evaluation.

RESULTS

The mean follow-up time was 42 months (18-108 months), three cases being lost to follow-up 18-27 months postoperatively. The HHS improved from 47.5 ± 8.7 to 88.5 ± 3.1. The mean length of femoral segments removed was 2.5 ± 0.8 cm (range, 1.0-4.5 cm) and mean acetabular inclination 43° ± 5° (range, 31°-54°). Caudalization of the femoral head center was 3.2 ± 3.0 mm (range, -3 to 12 mm) and lateralization 4.0 ± 4.0 mm (range, -9 to 11 mm). Mean greater trochanter height relative to theoretical hip center was 5.2 ± 1.0 cm (range, 3.5-7.1 cm) preoperatively and 0.2 ± 0.6 cm (range, -0.9 to 1.2 cm) postoperatively. Intraoperative trochanteric fractures occurred in three cases and sciatic nerve palsy in one.

CONCLUSION

THA with subtrochanteric femoral shortening osteotomy is an effective technique for treating high hip dislocation. Its advantages include improvement in limb imbalance and decreased risk of sciatic nerve injury.

Lesion of gluteal nerves and muscles in total hip arthroplasty through 3 surgical approaches. An electromyographically controlled study

PURPOSE

Three surgical approaches in total hip arthroplasty (THA) were compared concerning: 1) clinical and radiological results; 2) innervation of the tensor fasciae latae and gluteal muscles; 3) clinical outcome of the nerve lesions; 4) sensitivity of the EMG analysis.

METHODS

A total of 70 patients aged 39-79 years were evaluated clinically and electromyographically before and 3-9 months after THA in 2 centres using the anterolateral approach in 22, transgluteal approach in 33 and posterior approach in 15 patients, respectively.

RESULTS

1) Hip flexion, external rotation and Trendelenburg lurch were reduced and the centre of the rotation was higher after the anterolateral approach. 2) The inferior branch of the superior gluteal nerve of the tensor fasciae latae muscle was mostly damaged in the anterolateral approach (73% of lesions), whereas innervations of gluteus medius (9% of lesions) and maximus muscles (no lesion) were preserved. The transgluteal approach most often caused a partially denervated gluteus medius (81.8%) and the tensor fasciae latae (48%) and the gluteus maximus muscle only in 29%, respectively. After the posterior approach, partial denervation in the gluteus medius and maximus muscles were noted in 53.3% and 71.4%, respectively, whereas in the tensor fasciae latae muscle in only 14%. 3) The power of the abductors was not significantly reduced in partially denervated muscles. 4) The EMG examination is not sensitive enough to determine the relevant power of hip abductors.

CONCLUSIONS

Despite some disadvantages associated with the anterolateral approach, the transgluteal and posterior approaches are often connected with a partial lesion of the gluteus medius and maximus muscles. In all approaches, clinical sequelae are not significant in primary THA.

Neurolysis for the treatment of sciatic nerve palsy associated with total hip arthroplasty

Sciatic nerve palsy following total hip arthroplasty (THA) is a relatively rare yet potentially devastating complication. The purpose of this case series was to report the results of patients with a sciatic nerve palsy who presented between 2000 and 2010, following primary and revision THA and were treated with neurolysis. A retrospective review was made of 12 patients (eight women and four men), with sciatic nerve palsy following THA. The mean age of the patients was 62.7 years (50 to 72; standard deviation 6.9). They underwent interfascicular neurolysis for sciatic nerve palsy, after failing a trial of non-operative treatment for a minimum of six months. Following surgery, a statistically and clinically significant improvement in motor function was seen in all patients. The mean peroneal nerve score function improved from 0.42 (0 to 3) to 3 (1 to 5) (p < 0.001). The mean tibial nerve motor function score improved from 1.75 (1 to 4) to 3.92 (3 to 5) (p = 0.02).The mean improvement in sensory function was a clinically negligible 1 out of 5 in all patients. In total, 11 patients reported improvement in their pain following surgery. We conclude that neurolysis of the sciatic nerve has a favourable prognosis in patients with a sciatic nerve palsy following THA. Our findings suggest that surgery should not be delayed for > 12 months following injury.

Neurologic injuries after primary total ankle arthroplasty: prevalence and effect on outcomes

Background

Neurologic injuries are complications that can arise after total joint arthroplasty. However, no comprehensive study has been conducted on peripheral nerve injuries after total ankle arthroplasty. The purpose of the present study was to identify the prevalence of neurologic injury following primary total ankle arthroplasty, the predisposing factors, and evaluate the effect on clinical outcomes.

Methods

We retrospectively analyzed 150 consecutive primary total ankle arthroplasty using the mobile-bearing prosthesis between January 2005 and December 2011, in 150 patients with symptomatic ankle end-stage arthritis. All the patients were divided into groups according to whether they had postoperative peripheral neuropathy (23 patients) or not (127 patients). We investigated the prevalence, predisposing factors, and effect on clinical outcomes of neurologic injuries. The mean age was 61.3 years, and the mean follow-up period was 41.8 months.

Results

There were 23 nerve injuries (15.3 %), including nine in posterior tibial nerves, six superficial peroneal nerves, six deep peroneal nerves, one saphenous nerve, and one sural nerve. Neurologic injury was significantly associated with the development of posttraumatic osteoarthritis, but it was not significantly associated with other predisposing factors, such as age, gender, body mass index, and symptom duration. Of the 23 nerve injuries, 13 (56.5 %) presented a complete, spontaneous recovery, 9 (39.1 %) presented an incomplete recovery, and 1 (4.3 %) presented no recovery. The patients with neurologic injury had significantly lower American Orthopaedic Foot and Ankle Society scores and lower levels of patient satisfaction.

Conclusions

The results of this study suggest that the prevalence of neurologic injury after total ankle arthroplasty is considerable, and that neurologic injury is associated with low levels of patient satisfaction and poor clinical outcomes at mean of 3 years, postoperatively. Care is needed to reduce the occurrence of neurologic injuries.

Cementless Hip Arthroplasty in Southern Iran, Midterm Outcome and Comparison of Two Designs

BACKGROUND

Cementless hip prosthesis was designed to provide biologic fixation, without the use of cement. The second generation components have shown more reliable bone ingrowths and survival rates. We are reporting a midterm result of two designs of cementless prosthesis in a unique culture with different social habits and expectations.

METHODS

52 primary cementless total hip arthroplasty in 42 patients with the mean age of 48.8 years were retrospectively studied. Two groups of prosthesis had been implanted: Harris-Galante II (HGII) in 15 and Versys-Trilogy (V-T) in 37 hips, both from Zimmer company. The patients were assessed clinically, radiographically and with Harris hip score, SF36, WOMAC, and MACTAR questionnaires, with 65 months (26-136) mean follow-up.

RESULTS

All the V-T prostheses had survived well. Eight of HG II were revised by the last follow-up in 19-102 months. All had undergone acetabular revision and 2 combined with femoral revision. Broken tines of HGII cups were seen in 4 radiographs. The 65 months overall survival was 96.2% for femoral and 84.6% for acetabular components. 90% had good or excellent Harris hip scores. The functional scores were poorer in the HG II group. Pain relief and improved walking were the two main patients' expectations fulfilled in 97.6% and 92.8%, respectively.

CONCLUSIONS

The outcome of cementless total hip arthroplasty (THA) is satisfactory and comparable with the literature based on the results of function and survival of this small comparative group. The use of HGII acetabular component should be abandoned.

Complications Following Direct Anterior Hip Procedures: Costs to Both Patients and Surgeons

A systematic review of the literature on clinical outcomes following direct anterior approach (DAA) hip arthroplasty was performed. An aggregated 11,810 hip procedures were analyzed for intraoperative and early postoperative complications. The most common complication following DAA hip arthroplasty was nerve dysfunction (2.8%) followed by intraoperative fractures (2.3%). Postoperative dislocation, wound complications, and revision THA within the first 12 months were reported in 1.2% of cases. Thus, while DAA hip arthroplasty can be successfully performed, it is not without complications. Without definitive evidence of clinical superiority, surgeons considering switching to DAA should benchmark their personal complication rates against published reports.

Surgical approach in primary total hip arthroplasty: anatomy, technique and clinical outcomes

Total hip arthroplasty (THA) has revolutionized the treatment of hip arthritis. A number of surgical approaches to the hip joint exist, each with unique advantages and disadvantages. The most commonly used approaches include the direct anterior, direct lateral and posterior approaches. A number of technical intricacies allow safe and efficient femoral and acetabular reconstruction when using each approach. Hip dislocation, abductor insufficiency, fracture and nerve injury are complications of THA, although their relative risk varies by approach. Numerous clinical trials have sought to elicit differences in patient-reported outcomes, complication rates and return to function among the surgical approaches. This review outlines some of the technical pearls of performing a THA through either a direct anterior, direct lateral or posterior approach. A literature review outlines the impact of surgical approach on clinical outcomes and clinically relevant complication rates.

Sciatic Nerve Palsy Caused by Ruptured and Contracted Short External Rotator Muscles after Primary Total Hip Arthroplasty

Although the incidence of sciatic nerve palsy following total hip arthroplasty is low, this complication can cause devastating permanent nerve palsy. The authors experienced a case of sciatic nerve palsy caused by ruptured and contracted external rotator muscles following total hip arthroplasty in a patient suffering from osteonecrosis of the femoral head. We report this unusual case of sciatic nerve palsy with a review of the literature.

Total hip arthroplasty after previous fracture surgery

Total hip arthroplasty can be a very effective salvage treatment for both failed fracture surgery and hip arthritis that may occur after prior fracture surgery. The rate of complications is significantly increased including especially infection, dislocation, and loosening. Complications are more likely to occur after failed open reduction and internal fixation than after posttraumatic arthritis. Adequately ruling out infection before hip arthroplasty can be difficult. The best predictor of infection is a prior infection. Long-term outcomes can be comparable to outcomes in other conditions if complications are avoided.

A Rare Presentation of Sciatic Palsy Due to Hematoma After Use of the Kocher-Langenbeck Approach to the Acetabulum

CASE

A delayed sciatic palsy caused by compression due to hematoma formation is a rare complication of total hip arthroplasty. We report the case of a twenty-seven-year-old man who underwent open reduction and internal fixation of transverse and posterior wall acetabular fractures with posterior hip dislocation and had development of a delayed sciatic palsy due to the formation of a hematoma five days after the procedure.

CONCLUSION

A patient who presents with a delayed-onset sciatic palsy with signs and symptoms of a hematoma after an acetabular surgery represents a surgical emergency. Early recognition and urgent decompression offers the best chance of nerve recovery.

Sciatic nerve course in adult patients with unilateral developmental dysplasia of the hip: implications for hip surgery

Background

Sciatic nerve injury is a disastrous adverse complication of surgery and can cause debilitating pain, functional impairment and poor quality of life. Patients with developmental dysplasia of the hip (DDH) have a high incidence of sciatic nerve injury after total hip arthroplasty (THA). A better understanding of the course of the sciatic nerve in patients with DDH may help minimise the risk of sciatic nerve injury after THA.

Methods

A total of 35 adult patients with unilateral DDH were enrolled in this retrospective study. We reviewed the patients’ computed tomography (CT) scans, which included the area from the iliac crest to below the lesser trochanter. The distance between the sciatic nerve and regional anatomic landmarks in four different sections on CT scans was measured to identify the course of the sciatic nerve.

Results

The distance from the sciatic nerve to the spine’s midline was shorter on the affected side than on the healthy side (p < 0.05); the same difference was also detected in the distance to the ilium/ischium outside the true pelvis (p < 0.05). The distance to the greater trochanter was longer on the affected side (p < 0.05). However, the two sides showed no significant difference in the distance from the sciatic nerve to the lesser trochanter (p > 0.05).

Conclusions

For patients with unilateral DDH, the sciatic nerve was located near the ischium and ilium but relatively far from the femur of the affected hip joint, compared to its location on the healthy side. These findings reveal that sciatic nerve becomes shorter in the affected low-limb and is relatively unlikely to be directly injuried using the posterolateral approach in patients with unilateral DDH.

Neurovascular structure proximity to acetabular retractors in total hip arthroplasty

Neurovascular injury during total hip arthroplasty (THA) may result in considerable morbidity or mortality. The most common cause of intraoperative neurovascular injury during THA is retractor compression. Our aims were to: 1) determine proximity of common acetabular retractor positions during THA to adjacent neurovascular structures; and 2) determine effect of patient gender on these measurements. Retractor to neurovascular structure distances were measured on 32 preoperative computed tomography images and 16 cadavers. Our data suggest the anterior inferior iliac spine is the safest anterior acetabular retractor position. With inferior progression along the anterior wall, the distance to the femoral neurovascular bundle decreases. Due to its proximity to the sciatic nerve, the position of the posterior retractor should be monitored during acetabular preparation, particularly in women.

Total Hip Arthroplasty in Patient with the Sequelae of Legg-Calvé-Perthes Disease

Purpose

Patients who have secondary hip osteoarthritis as sequelae of Legg-Calvé-Perthes disease (LCPD) are severe deformities of femoral head and acetabulum. A few studies have presented that the clinical results and risks associated with total hip arthroplasty (THA) for patients with a history of LCPD were not satisfactory. In this study, we reported the radiographic and clinical outcomes of THA in patients with sequelae of LCPD.

Materials and Methods

Between March 2007 and May 2012, 23 hips (23 patients) underwent cementless THA and were followed up at least 2 years after surgery. There were 11 male patients and 12 female patients with an average age of 49.2 years old (range, 25 to 69 years old), and the average follow up period was 40.8 months (range, 24 to 84 months). The clinical and radiological evaluations were performed.

Results

The Harris hip score improved from 48.3 points preoperatively to 92.4 points at the time of the last follow-up. The shortening of affected limb was improved from -1.6 cm to 0.2 cm. The complications included one case of sciatic nerve palsy that developed after extensive lengthening of lower extremity, three cases of intraoperative femur fractures. There was no component loosening.

Conclusion

Fractures and motor nerve palsies may be more frequent in this population. Careful preoperative planning should be performed to overcome the technical pitfalls. If overcoming this early complication, the clinical and radiological evaluations showed excellent outcomes at average 40-month follow-ups.

[Blood vessel and nerve damage in total hip arthroplasty]

Blood vessel and nerve damage are uncommon complications in total hip arthroplasty (THA). With an incidence between 0.1 and 0.2 % in primary THA these complications are rare but can be serious with a high mortality risk. The individual risk is determined by multiple factors depending on the surgeon's skills, the number of previous surgeries and the approach itself. The anatomy of the defect is an essential risk factor. Some procedures, such as the use of screws for cup fixation are associated with a higher risk of vascular and neural damage. The acetabular quadrant system of the hip as described by Wasielewski et al. is a useful tool to visualize the neurovascular anatomy of the hip, to detect the safe zone and subsequently prevent complications. Sciatic nerve palsy after total hip replacement is the most common nerve damage followed by femoral nerve damage. Previous surgery, a posterior approach and excessive leg extension are the most common risk factors for nerve damage. In order to diagnose nerve palsy after orthopedic surgery an electromyogram can be of use to assess the extent and prognosis. This article focuses on vascular and neural complications after total hip arthroplasty and the options for diagnosis, treatment and prevention.

Long-term prognosis of nerve palsy after total hip arthroplasty: results of two-year-follow-ups and long-term results after a mean time of 8 years

INTRODUCTION

Nerve damage is a rare but serious complication after THA. There exist only little data about the outcome of these patients particularly regarding the long-term results later than 2 years postoperatively. Aim of this study is to answer the following questions: Is the recovery to be expected for light nerve lesions different from the severe ones? Is there a possibility of nerve recovery more than 2 years after THA? Is the potential of nerve recovery depending on the affected nerve?

MATERIALS AND METHODS

This study investigates 2,255 primary THA as well as revision surgeries performed from 1988 to 2003 relating to iatrogenic nerve lesion. We classified the nerve lesion according to the core muscle strength in severe (M0-M2) and light (M3-M4) nerve damage and differentiated between femoral, sciatic and superior gluteal nerve, according to the electromyography.

RESULTS

We found 34 cases of iatrogenic nerve damage representing an incidence of 1.5 %. 17 of 34 (50 %) patients showed a complete recovery after 2 years. Out of the remaining 17 patients, six out of seven patients with a final examination after a median time of 93 months achieved further improvement. The different nerves showed no significant different potential of recovery.

CONCLUSIONS

In contrast to the literature, an improvement beyond the limit of 2 years is probable and independent of the nerve affected.

Neurolysis for secondary sciatic nerve entrapment: evaluation of surgical feasibility and functional outcome

BACKGROUND

The study included 11 patients; seven males and four females with mean age of 68.3 ±11 years. All patients had sciatic nerve entrapment: three had a penetrating injury, three suffered postoperative trauma, two had a crush injury, two had inadvertent injections and one was trapped in a machine belt. Clinical examination included: an evaluation of the extent of motor and sensory impacts according to the British Medical Research Council (BMRC) scale and the Semmes-Weinstein monofilament test; assessment of pain sensation using the visual analogue scale (VAS); electromyography; and nerve conduction velocitiey determination. The applied operative procedure for sciatic neurolysis was modulated according to the suspected site of sciatic nerve entrapment. At 6 and 12 months after surgery all patients were evaluated for recovery of motor and sensory function.

RESULTS

All patients passed the smooth intraoperative course within a mean operative time of 77.7 ±21 min. The mean duration of wound drainage and postoperative hospital stay was 2.6 ±0.7 and 4.8 ±0.8 days, respectively. Pain sensation showed progressive significant improvement in nine patients but decreased at time of discharge and remained stationary till 12-m post-operative (PO). Recovery of motor function showed progressive significant improvement at 6 and 12 months after sciatic nerve neurolysis. The frequency of patients having muscle power recovery and regained sensation was significantly higher at 6-m and 12-m PO as compared to preoperative grading with a significantly higher frequency at the 6-m grading compared to preoperative grading. Two patients showed no change of their muscle strength grade, while nine patients showed improvement for a total success rate of motor strength recovery of 81.8%. At 6- m PO five patients showed no change of their sensory group, while six patients showed improvement for a total success rate of sensation recovery of 54.5%. At 12-m PO ten patients had fullly recovered protective sensation for a success rate of 90.9%.

CONCLUSION

Surgical exploration and neurolysis of cases with sciatic nerve entrapment is a safe and effective therapeutic modality with significant improvement of both motor and sensory functions without risk of additional deficit secondary to neurolysis.

Wake-up test in total hip arthroplasty with high-riding developmental dysplasia

Total hip arthroplasty (THA) for patients with Crowe type IV developmental dysplasia of the hip is technically challenging. This group of patients has a higher incidence of nerve injury during THA. Although neurophysiologic intraoperative monitoring has been developed to provide nerve monitoring, it is not always available. The wake-up test has been used for intraoperative spinal cord monitoring during major spinal surgery, but no study has reported the use of the wake-up test for neurologic monitoring during THA in patients with severe developmental dysplasia of the hip. The authors retrospectively reviewed 22 THA procedures in 20 patients with Crowe type IV developmental dysplasia of the hip who underwent the wakeup test during THA. In the current study, 1 patient could not dorsiflex her foot during the wake-up test. Therefore, the authors immediately reduced the length of limb lengthening by 1 cm. Postoperative drop foot and numbness occurred but resolved completely 2 months later. None of the patients who showed no deficits in motion of the feet during the intraoperative wake-up test had signs of postoperative nerve injury. In the current study, there was no false-positive or false-negative finding. The authors concluded that the wake-up test, which is simple, safe, and reliable, is a useful technique and a possible alternative to neurophysiologic intraoperative monitoring in checking nerve function during THA in patients with severe developmental dysplasia of the hip.

The role of retraction in direct nerve injury in total hip replacement: an anatomical study

OBJECTIVES

Acetabular retractors have been implicated in damage to the femoral and obturator nerves during total hip replacement. The aim of this study was to determine the anatomical relationship between retractor placement and these nerves.

METHODS

A posterior approach to the hip was carried out in six fresh cadaveric half pelves. Large Hohmann acetabular retractors were placed anteriorly, over the acetabular lip, and inferiorly, and their relationship to the femoral and obturator nerves was examined.

RESULTS

If contact with bone was not maintained during retractor placement, the tip of the anterior retractor had the potential to compress the femoral nerve by passing superficial to the iliopsoas. If pressure was removed from the anterior retractor, the tip pivoted on the anterior acetabular lip, and passed superficial to the iliopsoas, overlying and compressing the femoral nerve, when pressure was reapplied. The inferior retractor pierced the obturator membrane in all specimens medial to the obturator nerve, with subsequent retraction causing the tip to move laterally, making contact with the nerve.

CONCLUSION

Iliopsoas can only offer protection to the femoral nerve if the retractor passes deep to the muscle bulk. The anterior retractor should be reinserted if pressure is removed intra-operatively. Vigorous movement of the inferior retractor should be avoided. Cite this article: Bone Joint Res 2014;3:212-6.

Sciatic nerve injury related to hip replacement surgery: imaging detection by MR neurography despite susceptibility artifacts

Sciatic nerve palsy related to hip replacement surgery (HRS) is among the most common causes of sciatic neuropathies. The sciatic nerve may be injured by various different periprocedural mechanisms. The precise localization and extension of the nerve lesion, the determination of nerve continuity, lesion severity, and fascicular lesion distribution are essential for assessing the potential of spontaneous recovery and thereby avoiding delayed or inappropriate therapy. Adequate therapy is in many cases limited to conservative management, but in certain cases early surgical exploration and release of the nerve is indicated. Nerve-conduction-studies and electromyography are essential in the diagnosis of nerve injuries. In postsurgical nerve injuries, additional diagnostic imaging is important as well, in particular to detect or rule out direct mechanical compromise. Especially in the presence of metallic implants, commonly applied diagnostic imaging tests generally fail to adequately visualize nervous tissue. MRI has been deemed problematic due to implant-related artifacts after HRS. In this study, we describe for the first time the spectrum of imaging findings of Magnetic Resonance neurography (MRN) employing pulse sequences relatively insensitive to susceptibility artifacts (susceptibility insensitive MRN, siMRN) in a series of 9 patients with HRS procedure related sciatic nerve palsy. We were able to determine the localization and fascicular distribution of the sciatic nerve lesion in all 9 patients, which clearly showed on imaging predominant involvement of the peroneal more than the tibial division of the sciatic nerve. In 2 patients siMRN revealed direct mechanical compromise of the nerve by surgical material, and in one of these cases indication for surgical release of the sciatic nerve was based on siMRN. Thus, in selected cases of HRS related neuropathies, especially when surgical exploration of the nerve is considered, siMRN, with its potential to largely overcome implant related artifacts, is a useful diagnostic addition to nerve-conduction-studies and electromyography.

Perioperative lower extremity peripheral nerve traction injuries

Peripheral nerve traction injuries may occur after surgical care and can involve any of the lower extremity large peripheral nerves. In this review, the authors discuss injuries after knee or hip surgical intervention. The diagnosis, including electrodiagnostic studies, is time sensitive and also relies on a detailed history and physical examination. Successful prevention and treatment involve familiarity with risk and predisposing factors as well as prophylactic measures.

Common peroneal nerve palsy following total knee arthroplasty: prognostic factors and course of recovery

Common peroneal nerve palsy (CPNP) is a serious complication following total knee arthroplasty (TKA). There is little information regarding the clinical course and prognostic factors for recovery. Between January 2000 and December 2008, 44 patients (0.53%) developed CPNP following TKA and were matched to 100 control patients based on year of surgery, type of surgery and surgeon. Regression analysis was performed to identify prognostic factors for recovery. A significant difference was seen in CPNP patients who were on average younger (62.1 years) and had higher BMI (34.5 kg/m(2)) than those who did not have nerve palsy (67.5 years and 31.8 kg/m(2), respectively). Only 37 patients with palsies could be followed, 32 (62.2%) had incomplete nerve palsy, twenty four (75%) of them fully recovered, while only 1 of patients with complete nerve palsy fully recovered. More severe initial injury was a negative prognostic factor for recovery of palsy (P<0.03).

Total hip arthroplasty for the sequelae of Legg-Calvé-Perthes disease

BACKGROUND

The durability and risks associated with total hip arthroplasty (THA) for patients with a history of Legg-Calvé-Perthes disease (LCPD) are not well known.

QUESTIONS/PURPOSE

We sought to (1) determine the survivorship of THAs performed for LCPD; (2) assess hip scores and complications associated with THA in this patient population; and (3) compare results between patients who had undergone surgery in childhood with patients who had conservative treatment.

METHODS

We reviewed 99 primary THAs performed in 95 patients with a history of LCPD with minimum 2-year followup (mean ± SD, 8 ± 5 years). Mean age at THA was 48 ± 15 years.

RESULTS

A total of 10 revisions were performed. Using revision for any reason as the end point, the 8-year survival rate was 90% (95% confidence interval [CI], 76%-96%) for cementless implants compared with 86% (95% CI, 57%-96%) for hybrid implants. The mean Harris hip score improved by 31 ± 16 (n = 76). Complications occurred in 16% of hips. The most common major complication was intraoperative fracture (eight femoral, one acetabular). Three patients developed sciatic nerve palsy after a mean lengthening of 2.2 ± 1 cm compared with a mean of 1.4 ± 1 cm in patients with intact sciatic nerve (p = 0.3).

CONCLUSIONS

Cementless THAs for the sequelae of LCPD demonstrate 90% survival from any revision at 8 years followup. THAs for the sequelae of LCPD can be complicated and technically difficult. Intraoperative fractures and nerve injuries are common. Care should be taken to avoid excessive limb lengthening.

Total hip arthroplasty followed by traction and delayed reduction for Crowe IV developmental dysplasia of the hip

Hip dislocation secondary to developmental dysplasia of the hip is a debilitating condition. Total hip arthroplasty has proven successful in improving pain, restoring joint function, and correcting leg length discrepancies in this select population. Various techniques have been developed to address the increased complexity inherent to the reconstruction of the severely dysplastic hip. Despite this, femoral and/or sciatic nerve palsy remains a potential catastrophic complication after surgery, with reported rates up to five times that in the general population. We present three cases using a previously unreported technique for performing primary total hip arthroplasty via an anterior approach for Crowe IV hip dysplasia. The goal of this technique is to minimize the risk of postoperative nerve palsy following reconstruction of the severely dysplastic hip. A brief discussion of our technique and the topic of nerve dysfunction after total hip arthroplasty for developmental dysplasia of the hip follows.

[Femoral nerve palsy as delayed complication after total hip replacement: delayed hematoma formation in unexpected screw malpositioning]

Nerve injury after total hip replacement is a rare but severe complication. If the nerve lesion becomes evident in the early postoperative phase the lesion is often due to an incorrect implant position, direct nerve injury or vascular injury with manifestation of a hematoma which results in nerve compression. Secondary nerve lesions are more often due to a chronic hematoma with nerve compression. Secondary nerve lesions in particular are often a diagnostic challenge and should lead to an early revision after comprehensive imaging diagnostics.

Compression and entrapment neuropathies

Peripheral nerve entrapments are frequent. They usually appear in anatomical tunnels such as the carpal tunnel. Nerve compressions may be due to external pressure such as the fibular nerve at the fibular head. Malignant or benign tumors may also damage the nerve. For each nerve from the upper and lower limbs, detailed clinical, electrophysiological, imaging, and therapeutic aspects are described. In the upper limbs, carpal tunnel syndrome and ulnar neuropathy at the elbow are the most frequent manifestations; the radial nerve is less frequently involved. Other nerves may occasionally be damaged and these are described also. In the lower limbs, the fibular nerve is most frequently involved, usually at the fibular head by external compression. Other nerves may also be involved and are therefore described. The clinical and electrophysiological examination are very important for the diagnosis, but imaging is also of great use. Treatments available for each nerve disease are discussed.

Exploration and neurolysis for the treatment of neuropathic pain in patients with a sciatic nerve palsy after total hip replacement

The purpose of this study was to establish whether exploration and neurolysis is an effective method of treating neuropathic pain in patients with a sciatic nerve palsy after total hip replacement (THR). A total of 56 patients who had undergone this surgery at our hospital between September 1999 and September 2010 were retrospectively identified. There were 42 women and 14 men with a mean age at exploration of 61.2 years (28 to 80). The sciatic nerve palsy had been sustained by 46 of the patients during a primary THR, five during a revision THR and five patients during hip resurfacing. The mean pre-operative visual analogue scale (VAS) pain score was 7.59 (2 to 10), the mean post-operative VAS was 3.77 (0 to 10), with a resulting mean improvement of 3.82 (0 to 10). The pre- and post-neurolysis VAS scores were significantly different (p < 0.001). Based on the findings of our study, we recommend this form of surgery over conservative management in patients with neuropathic pain associated with a sciatic nerve palsy after THR.

Cite this article: Bone Joint J 2013;95-B:20–2.

Somatosensory evoked potential monitoring of peripheral nerves during external fixation for limb lengthening and correction of deformity in children

We undertook a retrospective analysis of 306 procedures on 233 patients, with a mean age of 12 years (1 to 21), in order to evaluate the use of somatosensory evoked potential (SSEP) monitoring for the early detection of nerve compromise during external fixation procedures for limb lengthening and correction of deformity. Significant SSEP changes were identified during 58 procedures (19%). In 32 instances (10.5%) the changes were transient, and resolved once the surgical cause had been removed. The remaining 26 (8.5%) were analysed in two groups, depending on whether or not corrective action had been performed in response to critical changes in the SSEP recordings. In 16 cases in which no corrective action was taken, 13 (81.2%, 4.2% overall) developed a post-operative neurological deficit, six of which were permanent and seven temporary, persisting for five to 18 months. In the ten procedures in which corrective action was taken, four patients (40%, 1.3% overall) had a temporary (one to eight months) post-operative neuropathy and six had no deficit. After appropriate intervention in response to SSEP changes, the incidence and severity of neurological deficits were significantly reduced, with no cases of permanent neuropathy. SSEP monitoring showed 100% sensitivity and 91% specificity for the detection of nerve injury during external fixation. It is an excellent diagnostic technique for identifying nerve lesions when they are still highly reversible.