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Leg lengthening and femoral offset reduction after total hip arthroplasty: where is the problem located – stem or cup?
Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences. (ortopedi)
Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences. Karolinska University Hospital - Department of Radiology.
Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences. Sundsvall and Norrland University Hospitals.
Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences. Sundsvall and Norrland University Hospitals.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Background and aims:

Restoration of the biomechanical forces around the hip with appropriate femoral offset (FO) and leg length is an important goal in total hip arthroplasty (THA). It is still controversial as to how much postoperative leg length discrepancy (LLD) and FO change are acceptable. The aim of this prospective study is to analyse whether the problem of postoperative leg lengthening and FO reduction is located in the stem or cup or both.

Material and methods:

Between September 2010 and April 2013, 174 patients with unilateral primary OA treated with THA were included. Postoperative LLD and global FO were measured using a standardized protocol of the antero-posterior hip radiograph. Patients whose operated leg became ≥ 10mm longer compared with the contralateral side (n=41) or reduction of the global FO > 5mm (n=58) were further studied to investigate the amount of leg lengthening and global FO reduction that took place in the stem and in the cup compared with the contralateral side. We compared the measurements made by an orthopaedic surgeon with the measurements made by a radiologist.

Results:

The leg lengthening was located in the stem while the FO reduction was located in both the stem and cup, for the two observers. For observer 1, the mean stem length of the operated side was 57.7 mm vs. 50.9 mm, p=0.003, while the mean cup length of the operated side was 19.0 mm vs. 18.9, p=0.95. For observer 2, the mean stem length of the operated side was 59.5 mm vs. 50.9 mm, p=0.001, while the mean cup length of the operated side was 18.2 mm vs. 18.8, p=0.90. The global FO reduction was located both in the stem and cup for the two observers. For observer 1, the mean stem offset of the operated side was 49.2 mm vs. 57.1 mm, p<0.001, while the mean cup offset of the operated side was 35.1 mm vs. 39.9, p<0.001. For observer 2, the mean stem offset of the operated side was 48.9 mm vs. 55.1mm, p<0.001, while the mean cup offset of the operated side was 35.5mm vs. 40.4mm, p<0.001. Both interobserver reliability and intraobserver reproducibility were substantial to excellent (ICC ≥ 0.79).

Conclusion:

Post THA lengthening of the operated leg is mainly caused by improper femoral stem positioning while global FO reduction results from improper positioning of both acetabular and femoral components. Surgeons should be aware of these observations in order to avoid them.

National Category
Surgery
Identifiers
URN: urn:nbn:se:umu:diva-114462OAI: oai:DiVA.org:umu-114462DiVA: diva2:895650
Available from: 2016-01-19 Created: 2016-01-19 Last updated: 2016-02-25Bibliographically approved
In thesis
1. Leg length discrepancy and femoral offset after total hip arthroplasty: clinical and radiological studies
Open this publication in new window or tab >>Leg length discrepancy and femoral offset after total hip arthroplasty: clinical and radiological studies
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Every year, about 1 million patients worldwide and 16000 patients in Sweden undergo total hip arthroplasty (THA). This surgical intervention is considered a successful, safe and cost-effective procedure to regain pain-free mobility and restore hip joint function in patients suffering from severe hip joint disease or trauma. Besides relieving the pain, restoration of biomechanical forces around the hip with appropriate femoral offset (FO), leg length and proper component position and orientation are important goals. The radiographic preoperative planning and postoperative evaluation of these parameters require good validity, interobserver reliability and intraobserver reproducibility. It remains controversial as to how much postoperative leg length discrepancy (LLD) and FO change are acceptable. Generally, lengthening of the operated leg ≥ 10mm and FO reduction of the operated hip > 5mm should be avoided by using preoperative radiological templating and intraoperative measurement methods. There is no consensus on the association between LLD and FO and outcome after THA.

The aims of this thesis were to:

1. To determine the influence of non-corrected LLD after THA on patients’ reported hip function and quality of life (QoL).

2. To study the association of global FO changes after THA with patients’ reported hip function, QoL and abductor muscle strength.

3. To evaluate the concurrent validity of the Sundsvall method of measuring postoperative global FO by comparing it to a standard method and to evaluate the interobserver reliability and intraobserver reproducibility of measurement of postoperative global FO, LLD and acetabular cup inclination and anteversion.

4. To analyse the postoperative radiographs of THA patients with leg lengthening and FO reduction to determine whether the problem is located in the stem, cup or both.

Study I: A prospective cohort study of 174 patients with unilateral osteoarthritis (OA), comparing patients with lengthening ≥ 10mm, restoration (between 9 mm lengthening and 5 mm shortening) or shortening > 5 mm of the operated leg after THA. Follow up was 12–15 months. We found that a LLD of up to 20 mm did not influence the functional outcome (WOMAC) or QoL (EQ-5D). However, the lengthening group showed less improvement in WOMAC and more use of a shoe lift.

Study II: A prospective cohort study of 222 patients with unilateral hip OA, comparing patients with decreased global FO (> 5 mm reduction), restored FO (within 5 mm restoration), and increased FO (> 5 mm increment) after THA. Follow up was was 12–15 months. The unadjusted results showed that the decreased FO group had a worse WOMAC index, less abductor muscle strength, and more use of walking aids. When these results were adjusted for possible confounding factors, only global FO reduction was statistically significantly associated with reduced abductor muscle strength. The incidence of residual hip pain and analgesics use was similar in the 3 groups.

Study III: A prospective cohort study of 90 patients with primary unilateral OA treated with THA. Global FO using the Sundsvall method, global FO (standard method), LLD, acetabular cup inclination and anteversion were measured on postoperative radiographs. The interobserver reliability and intraobserver reproducibility were tested using three independent observers. We found that the Sundsvall method is as reliable as the standard method and the evaluated radiographic measurement methods have the required validity and reliability to be used in clinical practice.

Study IV: A prospective cohort study of 174 patients with unilateral primary OA treated with THA. LLD and global FO were measured on postoperative radiographs. Patients with lengthening of the operated leg ≥ 10mm (n=41) and patients with reduction of global FO > 5mm (n=58) were further studied to investigate the amount of lengthening and global FO reduction that took place in the stem and in the cup compared with the contralateral side. The interobserver reliability and intraobserver reproducibility were tested using two independent observers. We found that post-THA lengthening of the operated leg ≥ 10mm was mainly caused by improper placement of the femoral stem, whereas a decrease of global FO > 5 was caused by improper placement of both acetabular and femoral components. The radiological measurement methods used showed substantial to excellent interobserver reliability and intraobserver reproducibility and are therefore clinically useful.

The main conclusions of this thesis are:

LLD up to 20 mm and reduced global FO more than 5 mm did not influence the functional outcome or quality of life at 12–15 months postoperatively.

Lengthening ≥ 10mm was associated with increased use of a shoe lift. A reduction of global FO more than 5 mm compared to the contralateral hip was associated with weaker hip abductor muscles and more use of walking aids. Therefore both should be avoided.

The radiographic measurement methods of LLD, global FO, cup inclination and anteversion have the required validity and reliability to be used in clinical practice.

Lengthening of the operated leg is mainly caused by improper femoral stem positioning while global FO reduction results from improper positioning of both acetabular and femoral components. Surgeons should be aware of these operative pitfalls in order to minimize component malpositioning.

Abstract [sv]

Varje år opereras ungefär 1 miljon patienter runt om i världen och 16000 patienter i Sverige med en total höftledsprotes (THA). Operation med höftledsprotes anses vara enav de mest framgångsrika, säkra och kostnadseffektiva kirurgiska åtgärderna med syfte att för att återställa livskvalité. Målet är att smärtlindra och återställa rörligheten i dendestruerade höftleden vid artros, reumatisk destruktion eller men efter exempelvis Perthes sjukdom. Vid operation med THA är det viktigt att återställa de biomekaniskakrafterna runt höftleden med en adekvat så kallad femoral offset (FO), postoperativ benlängdsskillnad (BLS) och ett tillfredsställande komponentläge. Den preoperativaplaneringen och den postoperativa bedömning av dessa parametrar kräver god tillförlitlighet, det vill säga validitet och reproducerbarhet både mellan olika bedömareoch vid upprepade mätningar av samma bedömare. Det är fortfarande inte klarlagt hur mycket postoperativ förändring i FO och BLS som är acceptabla. I dagsläget är detacceptabelt om den postoperativa benförlängningen understiger 1 cm och förändringen i FO är under 5 mm. Det finns ingen konsensus huruvida det föreligger ett sambandmellan BLS, FO och den patientrapporterade höftfunktionen och livskvalitén efter THA.

Syftet med denna avhandling var:

1. Att studera effekten av icke-korrigerad BLS efter THA på den patientrapporterade höftfunktionen och livskvalitén.

2. Att studera effekten av förändringen i FO efter THA på den patientrapporterade höftfunktion, livskvalitén och muskelstyrka i abduktion.

3. Att utvärdera validitet och reliabilitet av en så kallad global FO genom att jämföra den med den gällande standard metoden samt studera tillförlitlighet av de radiologiskamätningar av postoperativa BLS, FO, cup inklination och anteversion efter THA.

4. Att radiologiskt undersöka i vilken av komponenterna (stam eller cup) somförändringen i FO och BLS verkar vara förlagd.

Studie I: En prospektiv kohortstudie med 174 patienter som behandlats med THA för en primär unilateral koxartros. Patienterna delades in i tre grupper; de som fått en BLSförlängning över 10mm, återställning (mellan 9mm förlängning och 5mm förkortning) eller förkortning >5mm av det opererande benet efter THA. Uppföljning gjordes 12-15månader postoperativt. Vi fann att BLS upp till 20mm påverkade inte höftfunktion (WOMAC) och livskvalité (EQ-5D), men den förlängda gruppen visade en mindreförbättring i WOMAC och rapporterade en mer frekvent användning av skoinlägg.

Studie II: En prospektiv kohortstudie med 222 patienter som behandlats med THA för en primär unilateral koxartros. Patienterna delades in i tre grupper; de patienter medförminskad FO (> 5mm minskning), återställd FO (inom 5mm) eller ökad FO (>5mm ökning). Uppföljning genomfördes efter 1 år med WOMAC, styrkemätning av höftensabduktorer och en frågeformulär. En minskad FO var associerade med en minskad styrka i höftens abduktorer. Det var ingen skillnad mellan grupperna gällandekvarstående höftsmärta och användning av analgetika.

Studie III: En prospektiv kohortstudie med 90 patienter som behandlats med THA på grund av primär unilateral koxartros. På de postoperativa röntgenbilderna uppmättesglobala FO (Sundsvalls metodologi), globala FO (standard metod), BLS, cup inklination och anteversion. Reliabilitet och reproducerbarhet bedömdes mellan treoberoende observatörer. Vi fann att global FO (enligt Sundsvalls metodologi) är lika tillförlitlig som den nuvarande standardmetoden och de utvärderade radiologiskamätmetoderna har hög validitet och reliabilitet och kan således användas i klinisk praxis.

Studie IV: En prospektiv kohortstudie med 174 patienter som behandlats med en THA för en primär unilateral koxartros. På de postoperativa röntgenbilderna uppmättes BLSoch globala FO. Patienter med förlängning ≥ 10mm (n=41) och patienter med minskning av globala FO >5mm (n=58) studerades for att mäta förlängning ochglobala FO minskning som sitter i stammen eller i cup jämfört med kontralaterala sidan. Reliabilitet och reproducerbarhet bedömdes av två oberoende observatörer. Vifann att en BLS över 10mm sitter framför allt i stamkomponenten i lårbenet medan en minskning i FO över 5 mm sitter i båda stam och cup. De radiologiska mätmetodernahar hög reliabilitet och reproducerbarhet och kan således användas i klinisk praxis.

De viktigaste slutsatserna i denna avhandling är:

1. BLS med en förlängning upp till 20 mm och en minskning av globala FO mer än 5 mm påverkar inte patientrapporterad höftfunktion eller livskvalitet 1 år postoperativt.

2. BLS med en förlängning mer än 9 mm var associerad med mer användning av skoinlägg. En minskad FO med mer än 5 mm jämfört med den icke opererade höftenvar associerad med en sämre muskelstyrka i abduktion och ökat användning av gånghjälpmedel.

3. De radiologiska mätmetoderna av BLS, FO, acetabulära komponentens inklination och anteversion har hög validitet och reliabilitet, vilket kan användas i klinisk praxis.

4. En förlängning av det opererade benet orsakas främst av en positioneringen av stamkomponenten i lårbenet medan förlust av FO beror på otillfredsställande placeringav både stam och den acetabulära komponenten. Kirurger bör vara medveten om dessa operativa fallgropar för att optimera det kirurgiska resultatet.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 2016. 84 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1775
Keyword
Total hip arthroplasty, leg flength discrepancy, femoral offset, WOMAC, quality of life, complication, radiographic measurements, acetabular cup, inclination, anteversion
National Category
Clinical Medicine
Research subject
Orthopaedics
Identifiers
urn:nbn:se:umu:diva-114415 (URN)978-91-7601-394-6 (ISBN)
Public defence
2016-02-12, Aulan, Länssjukhuset Sundsvall-Härnösand, Länssjukhuset Sundsvall-Härnösand, Sundsvall, 09:00 (Swedish)
Opponent
Supervisors
Available from: 2016-01-22 Created: 2016-01-18 Last updated: 2016-02-02Bibliographically approved

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Mahmood, SarwarAl-Amiry, BariqMukka, Sebastian SSayed-Noor, Arkan S
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