412 THE BONE & JOINT JOURNAL

CHILDREN’S ORTHOPAEDICS

The treatment of an unstable slipped capital femoral epiphysis by either intracapsular cuneiform osteotomy or pinning in situA COMPARATIVE STUDY

R. D. M. Walton,E. Martin,D. Wright,N. K. Garg,D. Perry,A. Bass,C. Bruce

From Alder Hey Children’s Hospital, Liverpool, United Kingdom

R. D. M. Walton, FRCS, Orthopaedic SurgeonAlder Hey Children’s Hospital, 24 Dawlish Road, Irby, Wirral, CH612XP, UK.

E. Martin, MRCS, Specialist Registrar Pinderfields Hospital, Aberford Road, Wakefield, West. Yorkshire WF1 4DG, UK

D. Wright, FRCS, Orthopaedic SurgeonAlder Hey Children’s Hospital, Eaton Road, Liverpool L12 2AP, UK.

N. K. Garg, MS, MCh (Orth) , Orthopaedic Surgeon A. Bass, FRCS, Orthopaedic Surgeon C. Bruce, FRCS, Orthopaedic SurgeonAlder Hey Children’s Hospital, Eaton Road, Liverpool L12 2AP, UK.

D. Perry, FRCS, PhD, NIHR Clinical Lecturer, Warwick Clinical Trials UnitUniversity of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK.

Correspondence should be sent to Mr R Walton; e-mail: roger.walton@gmail.com

©2015 The British Editorial Society of Bone & Joint Surgerydoi:10.1302/0301-620X.97B3. 34430 $2.00

Bone Joint J 2015;97-B:412–19. Received 20 May 2014; Accepted 18 November 2014

We undertook a retrospective comparative study of all patients with an unstable slipped capital femoral epiphysis presenting to a single centre between 1998 and 2011. There were 45 patients (46 hips; mean age 12.6 years; 9 to 14); 16 hips underwent intracapsular cuneiform osteotomy and 30 underwent pinning in situ, with varying degrees of serendipitous reduction. No patient in the osteotomy group was lost to follow-up, which was undertaken at a mean of 28 months (11 to 48); four patients in the pinning in situ group were lost to follow-up, which occurred at a mean of 30 months (10 to 50). Avascular necrosis (AVN) occurred in four hips (25%) following osteotomy and in 11 (42%) following pinning in situ. AVN was not seen in five hips for which osteotomy was undertaken > 13 days after presentation. AVN occurred in four of ten (40%) hips undergoing emergency pinning in situ, compared with four of 15 (47%) undergoing non-emergency pinning. The rate of AVN was 67% (four of six) in those undergoing pinning on the second or third day after presentation.

Pinning in situ following complete reduction led to AVN in four out of five cases (80%). In comparison, pinning in situ following incomplete reduction led to AVN in 7 of 21 cases (33%). The rate of development of AVN was significantly higher following pinning in situ with complete reduction than following intracapsular osteotomy (p = 0.048). Complete reduction was more frequent in those treated by emergency pinning and was strongly associated with AVN (p = 0.005).

Non-emergency intracapsular osteotomy may have a protective effect on the epiphyseal vasculature and should be undertaken with a delay of at least two weeks. The place of emergency pinning in situ in these patients needs to be re-evaluated, possibly in favour of an emergency open procedure or delayed intracapsular osteotomy. Non-emergency pinning in situ should be undertaken after a delay of at least five days, with the greatest risk at two and three days after presentation. Intracapsular osteotomy should be undertaken after a delay of at least 14 days. In our experience, closed epiphyseal reduction is harmful.

Cite this article: Bone Joint J 2015;97-B:412–19.

The management of unstable slipped capitalfemoral epiphysis (SCFE) is contentious. Loderet al’s landmark paper1 highlighted avascularnecrosis (AVN) as the most feared complica-tion of this condition, with an incidence of47%. More recently, of the presence of femo-roacetabular impingement (FAI) has beenincreasingly recognised and in published serieshas led to total hip arthroplasty (THA) in theabsence of AVN. Dodd, McCormack andMulhall2 described 49 patients with stable andunstable SCFE, of whom 32% had clinicalsigns of FAI at 6.1 years. An operation that canrestore normal anatomy without increasing therisk of AVN has thus far proved elusive.

Whether an unstable SCFE should bereduced, and whether this should be closed,open, or open incorporating a shortening neckosteotomy, remains controversial. A survey of

members of the European Paediatric Ortho-paedic Society in 2011 revealed that, for unsta-ble severe slips, only 11% of members wouldadvocate an open reduction, whereas mostwould recommend closed reduction, eitherusing positioning on a routine operating table(46%), or more forcefully with traction andmanipulation (35%). Only 8% of membersindicated that they would deliberately avoidepiphyseal reduction.3 An equivalent surveywas conducted in America in 2005, with simi-lar findings, although 27% of respondents didnot routinely use the stable/unstable concept.4

There are several studies (Table I)5,6 docu-menting variable rates of AVN for unstableSCFEs treated by pinning in situ. Those studiespublished before Loder et al’s paper 1 include‘unstable equivalent’ hips and may not repre-sent the same pathological process. This

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includes Peterson et al’s paper,7 which is commonly quotedas the largest series of unstable SCFEs. Since 2000, fourseries have reported rates of AVN between 0% and 13%,8-11

although only the work of Parsch11 involved > 30 patients.It is likely that the true rate of AVN in unstable SCFEtreated by pinning in situ is not known.

Much has been written about the use of intracapsularosteotomy in patients with SCFE; however, this work per-tains predominantly to stable slips, with only two series ofunstable SCFEs (Table II).12 Rates of AVN of between 3%and 30% have been reported in the past, which many feelto be unacceptably high in patients who had a low predis-position to AVN at the time of presentation.13-18 Morerecently, surgical dislocation of the hip combined withcuneiform osteotomy has been described, with encouragingresults, although all but one series involved mainly stableSCFEs.19-22 One centre from Brazil has published prelimi-nary results of arthroscopic cuneiform osteotomy, with oneof a total of five patients developing AVN.23

Sankar et al22 have recently reported the use of a modi-fied intracapsular osteotomy, undertaken following surgi-cal dislocation of the hip, with an encouraging AVN rate of26% in 27 hips. There was also a 15% rate of implant fail-ure, although the method of fixation varied betweenpatients.

Biring, Hashemi-Nejad and Caterall24 reported a series of25 patients with SCFE, 23 of which were unstable. They weretreated with bed rest and ‘slings and springs’ for three weeks,followed by open cuneiform osteotomy without surgical dis-location. At a mean follow-up of eight years the rate of AVNwas 13%; chondrolysis was seen in 17%. The mean Iowa hipscore25 was 93.7/100, indicating a low incidence of FAI.

The timing of surgery for patients with unstable SCFE isalso controversial. Although the work of Peterson et al7

supports urgent intervention within 24 hours, this wasmeasured from the time of admission to hospital, ratherthan from the onset of symptoms. However, those hips thatwere pinned in situ developed AVN less frequently whentreated urgently. Other evidence is equivocal, with theseries of Loder et al1 conversely showing a higher rate ofAVN in urgently treated patients. There is no high-level evi-dence to guide the timing of surgery in these patients. Wehave previously proposed the concept of an ‘unsafe win-dow’ between 24 hours and one week. In our earlier retro-spective series of 16 unstable slips, eight developed AVN,all of whom underwent surgery within this period.26

Although Biring et al24 showed encouraging results whencuneiform osteotomy for unstable SCFEs was delayed for aminimum of three weeks, there was no comparison withthose undergoing this procedure earlier.

Table I. Evidence base for pinning in situ in unstable Slipped Capital Femoral Epiphysis and the incidence of avascular necrosis (AVN) accord-ing to the delay in presentation

Total no. of hips Capsulotomy Severity of slip % AVN < 24 h % AVN > 24 hrs Total % AVN

Casey 1972*5 23 No Mixed 66 15 22 Aadelen 1974*6 47 No Mixed 0 23 15 Loder 19931 30 No Mixed 80 40 47 Peterson 1997*7 91 No Mixed 7 20 14 Phillips 20018 14 No Mixed 0 - 0 Gordon 20029 16 Yes Mixed 0 33 13 Chen 200910 30 70% Mixed 13 - 13 Parsch 200911 64 Yes Mixed 5 - 5

* Includes assumed ‘unstable-equivalent’ cases

Table II. Evidence base for intracapsular osteotomy in stable and unstable Slipped Capital Femoral Epiphysis (SCFE) and theincidence of avscular necrosis (AVN) and chondrolysis

Study Total no. of hips Unstable SCFE Severity of slip AVN (%) Chondrolysis

Hagglund 198613 33 - All severe 30 - Fish 199414 66 - Mixed 3 5 De Rosa 199615 27 - All severe 15 - Velasco 199816 60 - Mixed 12 13 Fron 200017 50 - All severe 14 - Barros 200018 23 - All severe 13 Biring 2006*24 25 23 All severe 13 17 Leunig 2007†19 30 - Mixed 0 - Lawane 200912 25 - All severe 16 12 Slongo 2010†20 23 3 Mixed 7 - Akkari 2010‡23 5 - All severe 20 - Huber 2011†21 30 3 Mixed 3 - Sankar 2013†22 27 27 Mixed 26 -

* Three weeks pre-operative treatement with ‘slings and springs’ † With surgical dislocation ‡ Arthroscopic

414 R. D. M. WALTON, E. MARTIN, D. WRIGHT, N. K. GARG, D. PERRY, A. BASS, C. BRUCE

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Pinning in situ remains the popular approach for unsta-ble SCFE, presumably due to the perceived lower incidenceof AVN and shorter operating time.3,4 Both in theory andwith some evidence from Biring et al,24 intracapsular oste-otomy offers the potential to restore the anatomical rela-tionships of the proximal femur towards normality, whichmay theoretically reduce the incidence of FAI and subse-quent degenerative change. There is little evidence concern-ing both methods of treatment; in particular, there is nocomparative evidence to ascertain whether the perceivedhigh risk of AVN after intracapsular osteotomy is a reality.The question of the timing of surgery in unstable SCFE isunanswered.

The aim of this study was to compare the outcome ofintracapsular osteotomy with pinning in situ in patientswith an unstable SCFE. In addition, comparative data

concerning the timing of surgery of both forms of treatmentis discussed. The null hypotheses were that the rate of AVNis the same after both forms of treatment, and that the tim-ing of treatment does not affect the rate of AVN after eitherform of treatment.

Patients and MethodsThis was a retrospective single-centre comparative study.The medical records of 226 consecutive patients who pre-sented to our institution with a diagnosis of SCFE between1998 and 2011 were initially reviewed. In all cases the dateof presentation was after the publication of the paper byLoder et al,1 and none were excluded.

Although some patients had a prodromal period of lesssevere symptoms, care was taken to establish the time atwhich each patient became unable to bear weight, accord-ing to the definition of stability described by Loder et al.1

This was taken as a marker from which the timing of theoperation was taken.Surgical technique. Intracapsular osteotomy was employedaccording to the preference of the surgeon, when it wasdeemed that there would be significant technical difficultiesto undertake pinning in situ. For intracapsular osteotomy,patients were gently positioned supine on a traction tableand a standard anterior surgical approach with an ‘H’-shapedcapsulotomy was used. A metaphyseal trapezoidal sectionwas removed in slices, taking great care to respect the pos-terior vasculature. The physis was meticulously excised onboth sides of the osteotomy and the epiphysis was gentlyreduced under fluoroscopic guidance. Stabilisation wasachieved with one partially threaded cannulated screw.Patients were advised to remain non-weight-bearing for 12weeks post-operatively. Intra-operative photographs andradiographs are shown in Figures 1 to 4.

Patients treated by pinning in situ were positionedsupine, with or without the use of a traction table, with nodeliberate attempt at reduction, and one cannulated screw

Fig. 1

Intra-operative photograph showing surgical positioning for intracap-sular osteotomy.

Fig. 2

Intra-operative photograph showing ‘H’-shaped capsulotomy duringsurgery.

Fig. 3

Intra-operative photograph showing the site of the osteotomy.

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was introduced percutaneously. No capsulotomy or capsu-lar aspiration was undertaken.

AVN appeared on plain radiographs (AP pelvis +/- frogleg lateral) as fragmentation and collapse of the capital fem-oral epiphysis. AVN was defined as ‘total head involve-ment’ or ‘sectoral’ following retrospective review of thelatest follow-up radiographs and full agreement by the sen-ior authors (AB and CB). Statistical analysis. The incidence of AVN was comparedbetween the two surgical techniques using Pearson’s chi-squared test, with p = 0.05 taken to represent significance.Pearson’s chi-squared test was also used to analyse the inci-dence of right- versus left-sided slips. Means with range areprovided, where appropriate.

ResultsIn all, there were 46 unstable SCFEs in 45 patients, asdefined by the criterion of Loder et al:1 ‘unable to bearweight with or without crutches’. The mean age of thepatients was 12.6 years (9 to 14), and gender distributionwas even. There was a significant preponderance of left-sided slips (p = 0.03, Pearson’s chi-squared test) (Table III).

A total of 16 patients underwent intracapsular osteo-tomy and 30 underwent pinning in situ. Although no delib-erate attempt at reduction was made in the latter group, allslips reduced serendipitously to varying extents. This wascomplete in six patients and incomplete in 24.

In the intracapsular osteotomy group, no patient was lostto follow-up, which was undertaken at a mean of28 months (11 to 48). In one patient in each group it wasnot possible to determine the onset of instability, and sothese two patients were not included in the analysis of tim-ing to surgery.

Four patients in the pinning in situ group were lost tofollow-up, which was undertaken at a mean of 30 months(10 to 50). There was no difference noted in demographicsor the side of the SCFE between the groups (Table III).

For the entire cohort of patients the rate of AVN was36% (15/42) following adjustment for those lost to follow-up. Of the 16 SCFEs treated by intracapsular osteotomy,AVN developed in four hips (25%). In contrast, of the26 SCFEs treated by pinning in situ, AVN developed in11 (42%). This difference was not significant (p = 0.2556).The pinning in situ group was stratified by the extent ofserendipitous reduction. Following adjustment for thoselost to follow-up, complete reduction led to AVN in four offive hips (80%) and in seven of 21 (33%) in which reduc-tion was incomplete. The rate of the development of AVNwas significantly higher in those treated by pinning in situwith complete reduction, than in those treated by intra-capsular osteotomy (80% vs 25%) (p = 0.048, Pearson’schi-squared) (Table IV).

The degree of AVN was typically total head involvementin both groups. One of four hips with AVN in the intraca-psular osteotomy group and one of 11 hips with AVN in thepinning in situ group involved the superolateral quadrantexclusively.

A total of 11 patients underwent further surgery. Inten patients, this was in relation to AVN and in an addi-tional case, due to a secondary fracture at the site of thescrew which required screw exchange. Screw removal alonewas carried out in five patients. Two patients underwentscrew removal, followed by hip distraction with an externalfixator and a subsequent pelvic support osteotomy. In one,screw purchase was lost and revision fixation with twoscrews was required. One patient underwent screw

Fig. 4b

Anteroposterior (a), and anteroposterior and lateral (b and c) radiographs following osteotomy with the stabilising screw in situ.

Fig. 4a Fig. 4c

Table III. Study group demographics

Age (mean, range)

Gender(% male:female) Side (n) (% left)

Intracapsularosteotomy

12.6 (10 to 14) 47:53 12 (75)

Pinning in situ 12.6 (9 to 14) 53:47 21 (70)Total 12.6 (9 to 14) 50:50 33 (72)

Table IV. Effect of treatment on the development of avascularnecrosis (AVN) and further surgery (following adjustment forcases lost to follow-up

Procedure Total AVN Further surgery

Intracapsular osteotomy (16) 4 (25) 3 (18.8)Pinning in situ (26) 11 (42) 8 (31)Pinning in situ and incomplete reduction (21)

7 (33.3) 4 (19)

Pinning in situ and complete reduction (5)

4 (80) 4 (80)

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removal, followed by hip distraction with an external fixa-tor and concurrent excision arthroplasty with gluteal inter-position. A final patient was treated with screw removaland subsequent valgus femoral osteotomy.

In some patients, the unstable SCFE occurred after a pro-dromal period of symptoms. The sample was further sub-analysed for ‘acute’ versus ‘acute-on-chronic’ slips. Therewere a total of 29 acute SCFEs and 12 acute-on-chronicSCFEs, and in five SCFEs there was insufficient informationto assess the chronicity.

In all, 11 hips (69%) treated with intracapsular osteo-tomy and 18 (72%) of those treated by pinning in situ (aftercorrecting for those with insufficient documentation) wereacute. Of the five hips treated by pinning in situ with com-plete reduction and sufficient follow-up, four were acute.There was no association between the chronicity of symp-toms and the incidence of AVN (p = 0.5762, Pearson’s chi-squared test). In the intracapsular osteotomy group, threeof 11 acute cases and one of five acute-on-chronic casesdeveloped AVN. In the pinning in situ group, eight of 16acute cases and two of six acute-on-chronic cases developedAVN. Of those with complete reduction, only one did notdevelop AVN; this was an acute slip.

Heterotopic ossification and meralgia paraesthetica werecomplications particular to intracapsular osteotomy, bothseen in two hips (12.5%). Heterotopic ossification wasdiagnosed on plain imaging following agreement by thesenior authors (AB and CB). This was symptomatic in onepatient, with symptoms resolving after treatment with oralindomethacin. One patient treated by pinning in situ suf-fered a fracture of the femoral neck at the site of entry of thescrew, eight months following the initial procedure. Thisrequired further fixation.

With respect to the timing of surgery, intracapsularosteotomy was carried out at a mean of 12.1 days (7 to 25)after unstable symptoms began. The four hips treated inthis way that developed AVN underwent surgery at a meanof 9.75 days (7 to 13) after unstable symptoms began. Thepatient who underwent surgery 13 days after unstablesymptoms began and developed AVN failed to comply withpost-operative non-weight-bearing instructions. Of the fivehips that were treated > 14 days after unstable symptomsbegan, none developed AVN, although these differenceswere not statistically significant (p = 0.0986, Pearson’s chi-squared test) (Table V).

In 12 SCFEs pinning in situ was undertaken preferen-tially on an emergency basis, within 24 hours of unstablesymptoms. Surgery in the remaining patients was under-taken between 24 hours and eight days after unstable symp-toms began this delay being for logistical reasons or due todelayed presentation, particularly during the early years ofthe study, which includes patients reported in our earlierpaper.26 Following adjustment for those lost to follow-upand without adequate documentation of the onset of symp-toms, the rate of development of AVN in those treated byemergency pinning in situ was 40% (four of ten) compared

with 47% (four of 15) in those treated by non-emergencypinning in situ. The highest rate of AVN was seen in thosetreated two or three days after unstable symptoms began(4/6; 67%). There was no significant difference in the rateof development of AVN or reoperation, depending on thetiming of surgery (Table VI).

Complete reduction occurred almost exclusively whenpinning in situ was used as an emergency (6/14 hips; 43%)and was only seen once in non-emergency cases (6%). Thisdifference approached significance (p = 0.056, Pearson’schi-squared test). Of the 12 SCFEs treated as an emergency,five had complete reduction; one was subsequently lost tofollow-up and the remaining four developing AVN. A totalof seven SCFEs reduced incompletely, with one being lost tofollow-up; none of the remaining six developed AVN.Emergency pinning in situ with complete reduction wasstrongly predictive for AVN, compared with emergencypinning in situ with incomplete reduction (p = 0.005,Pearson’s chi-squared test).

DiscussionIt has recently been shown that intracapsular osteotomymay limit the development of FAI after the treatment of astable SCFE, with some evidence suggesting that this mayalso be the case for unstable SCFEs.22,24 In this study wehave shown that, in our hands, intracapsular osteotomydoes not have an increased rate of AVN compared with pin-ning in situ in patients with an unstable SCFE. Further-more, and strikingly, it appears that intracapsularosteotomy may have a protective effect on the vasculatureof the femoral head. This finding reached significance whenthe intracapsular osteotomy group was analysed againstthe pinning in situ subgroup with complete reduction(p = 0.0271, Pearson’s chi-squared test). Our findings sup-port those of Biring et al24 and Sankar et al.22 Whereas thelatter authors undertook osteotomy via surgical dislocationof the femoral head, we have described an acceptable alter-native method, with equivalent results.

Table V. Effect of the timing of surgery in the intraca-psular osteotomy group (following adjustment) andthe development of avascular necrosis (AVN)

Timing of procedure following onset of instability Rate of AVN (%)

Days 7 to 13 (10) 4 (40)Day 14 onwards (5) 0

Table VI. Effect of the timing of surgery in the pin-ning in situ group (following adjustment) and thedevelopment of avascular necrosis (AVN)

Timing of procedure followingonset of instability Rate of AVN (%)

Within 24 hours (10) 4 (40)Days 2 to 3 (6) 4 (67)Day 5 onwards (9) 3 (33)

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The ideal treatment for an unstable SCFE would restorethe normal anatomy, avoid FAI and achieve a low rate ofAVN. It seems that intracapsular osteotomy might reduce theincidence of both FAI and AVN. Intuitively, an openapproach, capsulotomy and instrumentation of the femoralneck would put the vasculature at risk. However, we suggestthat our findings are rational. Opening the capsule mayremove the tamponade effect; Herrera-Soto et al27 havereported a twofold rise in intracapsular pressure in SCFE anda threefold rise if the epiphysis is reduced. Relief of intracap-sular pressure may enable greater blood flow to the epiphy-sis, and anatomical restoration of the neck may resolvekinking and tension on the vessels. Finally, complete excisionof the physis may remove a barrier to the ingrowth of meta-physeal vessels and allow revascularisation. There is someevidence to suggest that the severity of the slip is an inde-pendent predictor of AVN.28 This would suggest that all ourpatients who underwent intracapsular osteotomy had an ini-tially higher predisposition to AVN, as this procedure waspredominantly undertaken in hips in which the severity ofthe slip was felt to make pinning in situ technically difficult.With this in mind, our results are all the more striking.

All patients treated by pinning in situ underwent seren-dipitous closed reduction to some extent, in an unpredicta-ble fashion. When closed reduction was complete, the ratesof AVN were higher. Complete reduction was more likely tooccur within the first 24 hours after presentation. Closedreduction and pinning in situ has been shown to befavoured in Europe as recently as 2011.3 Our experienceraises questions regarding this practice. We suggest thatimaging of an unstable SCFE represents a snapshot of adynamic process. Physeal instability results in a mobile epi-physis, leading to serendipitous reduction. We feel that phy-seal instability is probably a continuum, rather thanobeying the binary classification described by Loder et al.1

It is likely that an unknown determinant in the pathophys-iology of SCFE leads to more significant physeal instabilityin some hips, which are subsequently more prone to phy-seal mobility, serendipitous reduction and AVN. It isunclear whether the propensity to develop AVN is causedby serendipitous reduction, or whether this is a marker ofmore significant underlying instability, which in itself mayhave a tendency to a poor outcome.

Capsulotomy was not performed in the hips we treatedby pinning in situ; in retrospect, this may be a usefuladjunct and may explain why the results of pinning in situare not as favourable as in some previous series, in whichcapsular decompression was performed in some form.9-11

We note that some of those series contained ‘unstable-equivalent’ hips. We have detailed our belief that physealinstability represents a continuum. It is, however, currentlyimpossible to determine where a patient lies along this spec-trum and comparison of our results with others may beinappropriate due to heterogeneity within and betweenseries. From two series of 16 and 30 patients, respectively,Gordon et al9 and Chen et al10 have suggested that

emergency pinning in situ, combined with capsulotomy foran unstable SCFE has a low rate of AVN. Parsch et al11

achieved a low rate of AVN of 4.7% in a larger group of64 unstable SCFEs. In contrast to other published series,Parsch’s group11 performed emergency open reduction,without osteotomy, and fixed the epiphysis with multipleKirschner wires. It is possible that any potential benefit ofemergency pinning in situ was masked in our series by thelack of formal capsulotomy. In this subgroup in our studythe distinction between good and poor outcomes seems tobe governed by the degree of epiphyseal reduction. The hipswith complete reduction had a very poor outcome and mayhave stood to gain most from capsular decompression.There has previously been difficulty in determining whetheremergency timing or formal capsulotomy is the major fac-tor determining the good results reported by Parsh et al:11

our findings would suggest it to be the latter.When osteotomy was delayed for a minimum of two

weeks from the onset of symptoms, our results concur withthose of Biring et al24 and Sankar et al,22 who have pro-vided the only other data concerning intracapsular osteo-tomy in unstable SCFE. Biring et al24 advocate a pre-operative delay of at least three weeks. In our experience,intervention between the seventh and 14th days after pres-entation is harmful, representing an ‘unsafe window’ of rel-ative epiphyseal vulnerability. We suggest that, followingthis period, the physis stabilises to some degree, making theintervention more benign. We did not study the effect ofintracapsular osteotomy undertaken within one week ofthe development of symptoms. Parsch et al11 have providedrobust data to suggest that emergency open reduction,without osteotomy, is beneficial; it would follow that emer-gency intracapsular osteotomy may also be beneficial.

Our earlier study discussed the concept of an ‘unsafewindow’ for pinning in situ in unstable SCFE between twoand seven days after the onset of symptoms.26 In this up-to-date and larger series, surgery two or three days after pres-entation seems to be particularly contraindicated. We haveno data for the fourth day after presentation, and have con-sequently defined an updated ‘unsafe window’ as betweenthe second and fifth days.

Emergency pinning in situ in unstable SCFEs requires re-evaluation. In the absence of complete closed reduction,results appear to be reasonable. However, we found thatcomplete closed reduction without decompression is morelikely in the emergency setting and leads to poor results. Wehave discontinued the practice of emergency closed pinningin situ in favour of an emergency open reduction, ordelayed intracapsular osteotomy.

This series included a significantly higher number of left-sided SCFEs (p = 0.03). We suggest that this may beexplained by a predominance of right-foot-dominant indi-viduals. As seen in sporting activities, these patients leadwith their left foot during a sharp forward movement.Studies of anterior cruciate ligament injuries have shownthat limb dominance is predictive for the injured side.29,30

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There is currently little information about the use ofintracapsular osteotomy in unstable SCFE. Comparison ofexisting series of intracapsular osteotomy and pinning insitu is fraught with error, as a result of differing methodol-ogies and heterogeneous groups. This first comparativestudy of unstable SCFE is therefore a worthwhile additionto the evidence base and raises questions of current opin-ion. Since the work of Parsch et al,11 this represents the sec-ond largest study of unstable SCFEs without ‘unstable-equivalent’ cases.

There are shortcomings to this study, which could beaddressed to produce more robust data in forthcomingpapers. The retrospective methodology is common to mostof the literature on unstable SCFEs. We were unable toachieve a complete data set, due to shortcomings with doc-umentation and follow-up, although full data were availa-ble to calculate the rates of AVN in 91% of cases and theeffect of surgical timing in 87%. Although we have pre-sented a large number of patients with this rare condition,the subgroups with respect to intervention and the timingof surgery are small.

In our experience, the chronicity of symptoms was notpredictive of the development of AVN. It is, however,likely that the practice of reducing an acute-on-chronicSCFE to a position beyond that in which it lay during itschronic phase would be detrimental. We may have insuf-ficient numbers in our subgroups to have demonstratedthis. We feel that an open early reduction, or late intraca-psular osteotomy, may be of benefit in this situation toprevent over-reduction.

We were unable to determine whether AVN was prede-termined in some hips by the nature of the pathology, orwhether it developed because of the intervention. Someunits use pre-operative MRI and intra-operative blood flowmeasurements.31-33 These additions might add to the relia-bility of the data produced.

The key to a good outcome in unstable SCFE remainselusive: it may depend on capsular decompression, the res-toration of normal anatomy, the exact nature of the surgicalprocedure, or its timing. A prospective randomised multi-centre trial is strongly indicated to test those interventionsthat have been shown to have more favourable outcomes,such as emergency open reduction as reported by Parschet al,11 and delayed intracapsular osteotomy as reportedhere and by Biring et al24 and Sankar et al.22

Author contributions

R. D. M. Walton: Implementation and design of the study, Data collection andanalysis, Writing of the paper.E. Martin: Data collection and analysis. Writing of the paper.D. Wright: Data analysis. Writing of the paper.N. K. Garg: Data collection and analysis. Writing of the paper.D. Perry: Statistical analysis. Writing of the paper.A. Bass: Review of radiographs. Writing of the paper.C. Bruce: Review of radiographs. Writing of the paper.

No benefits in any form have been received or will be received from a commer-cial party related directly or indirectly to the subject of this article.

This article was primary edited by J. Scott and first proof edited by G. Scott.

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