J Med Allied Sci 2018; 8(2):78-85 DOI: 10.5455/jmas.288082

Original article

The effects of resisted hip abductor strengthening in initial phase in patients with hip arthroplasty

Rutika Sureja1, Niketa Patel2, Lata Shroff Parmar2, Paresh Golwala3

Affiliation(s):

1C2-401, Golden Park, Street near to Indian Oil Petrol Pump, Near Dipanjali, Timbavali, Junagadh-362015, Gujarat, India.

2College of Physiotherapy, Sumandeep Vidyapeeth, Waghodia, Vadodara-391750, Gujarat, India.

3Department of Orthopedics, Smt. B. K. Shah Medical Institute and Research Centre, Sumandeep Vidyapeeth, Waghodia, Vadodara-391750, Gujarat, India.

Corresponding author: Prof. Lata Shroff Parmar, Principal, College of Physiotherapy, Sumandeep Vidyapeeth, Waghodia, Vadodara-391750, Gujarat, India.

Phone: +91-9825825578 Email: principal.physiotherapy@sumandeepvidyapeethdu.edu.in

Abstract

Although hip arthroplasty (HA) is done to effectively reduce pain and improve mobility and hence quality of life (QOL), this may not effectively restore biomechanics and improve gait as strength of hip muscles have been reported to remain weaker when assessed after 1 year of HA. Several studies done for assessing effects of strengthening exercises for varying periods at follow-ups of different intervals have been reported. This study was done to assess the effects of resisted hip abductors program given in initial phase following total hip arthoplasty (THA). Consecutive patients of HA referred for physiotherapy satisfying inclusion criteria were recruited (N=15). Patients were divided in 2 groups. Control group (N=7) given conventional therapy and experimental (N=8) given conventional therapy and resisted isometric hip abductor strengthening. Harris hip score (HHS) and strength measurement with modified sphygmomanometer (MoS) was recorded in each group, on the 3rd and 8th post-operative day (POD). Normal individuals (N=30) with comparable age and gender were studied to estimate the hip abductor strength with MoS. 11 of total cases were following hip fracture, 4 were AVN. On 3rd POD both groups were similar for age, gender, strength and HHS. Both groups on 3rd day had mean strength 31.87±4.57 (mean of normal 101.4±12.80) mm of Hg. Strength and HHS within groups improved significantly (p<0.001) on 8th POD. However, mean difference in strength was statistically significant in experimental group compared to control group (p=0.016), no significant difference seen in HHS (p=0.70). The study concludes that resisted isometric hip abductor strengthening exercises started early along with conventional physiotherapy are beneficial.

Keywords: Hip arthroplasty, Hip muscles strengthening, Resisted hip abductors, Total hip arthroplasty

Running title: Resisted hip abductor strengthening in hip arthroplasty

Introduction

In the lower extremity reconstruction surgeries, one of the most advanced reported surgeries worldwide is the hip arthroplasty. It is said to be ‘operation of the century’1,2. In India itself 70,000 joint replacement surgeries are said to be performed annually3.

In general, there is preference for uncemented type of arthroplasty for the young and active and cemented implant for the older population and worse bone structure3,4. Osteoarthritis of hip, a vascular necrosis, ankylosing spondylitis, failed fracture / dislocations of hip are the main indications for hip replacement surgery3. Hip replacement surgery approaches are classified based on their location relative to the anatomic structures.

The difference between the anterior and anterolateral is that one avoids compromising the hip abductor function as the incision is placed between the sartorius and tensor fascia latae while the antero-lateral exposes the gluteus medius5,6. However, commonly used incisions are ‘Lateral approaches’, either anterolateral, lateral or postero-lateral and  of these all require at least partial detachment of the glutei, but of these anterolateral and lateral lead more to hip abductor weakness and posterolateral shows increased tendency of dislocation5-10.

Although hip arthroplasty is done to effectively reduce pain and improve mobility and hence the quality of life11-14, this however may not effectively restore biomechanics and improve gait15,16 as strength of hip muscles i.e. hip abductors, extensor and flexors have been reported to be weaker when assessed even after 1 year of hip arthroplasty12,14,15,17-19.

The gluteus medius and minimus are primarily responsible for stabilising pelvis in unilateral stance, preventing pelvic drop. Due to hip muscles weakness especially, the hip abductors post total hip arthroplasty (THA) the lateral stability may be compromised associated with poor trunk control during body weight transfer from the operative to the non-operative lower extremity leading to balance problems20-22. Jogi et al reported one in four patients to have a fall within 2 years following THA surgery23.

Long term mild to moderate disabilities viz. pain, muscle weakness of hip abductors leading to loosening and joint instability, contracture of hip joint and gait disorders have been reported in patients post hip replacement15,17.

Post operatively the patients following hip arthroplasty are referred for physiotherapy immediately by the 2nd POD and are made ambulant as soon as it can be possible. The hospital stay usually is not long, maximum extending to 10-15 days, if there is no complication. As the patient is already ambulant by 2nd day the concentration on specific strength component is invariably overlooked, thus in the long term problems associated with Hip Abductor weakness persists even though the overall functions are unaffected.  

This study was planned to see if initial strength building program in addition to the walking made any difference to overall function of these patients at the point of discharge. The aim was to study effects of resisted hip abductors strengthening program on strength and function, given in initial phase in patients following hip arthroplasty. The objectives were to study the effects of resisted hip abductors strengthening exercises by modified Sphygmomanometer (MoS) and to study the effects of resisted hip abductors strengthening on functional outcome by Harris hip score (HHS).

Materials and methods

The proposed study was approved by the Institutional Ethical Committee of the University - Sumandeep Vidyapeeth Institutional Ethical Committee; approval number- SVIEC/ON/PHYS/BNMPT15/D1600 dated 12th March 2016.

Research design: Interventional, non-randomized control trial. Allotment was on alternate basis as consecutive patients were to be included.

Source of data: Dhiraj General Hospital

Sample size: All consecutive patients of hip replacement referred for physiotherapy

Pilot study for normative data was done. Normal healthy (self-declared) individuals with comparable age and both gender for this were 30 i.e. 60 legs (both limbs). The hip abductor strength with Sphygmomanometer was established.

Inclusion criteria

  Subjects following hip arthroplasty after they are referred for physiotherapy

  Adults >18 years

Exclusion criteria

  Subject with spine and lower limb pathology

  Subject with neurological disorder related to lower limb

  Unwillingness to participate

Tools and materials

1.   Sphygmomanometer (Fig 1)

2.   HHS questionnaire

Fig 1. Sphygmomanometer (aneroid manometer)

Methodology

After obtaining approval from Institutional Ethical Committee, consecutive patients with hip arthroplasty referred for physiotherapy were recruited for the study. Patients were explained about the study, and informed consent was obtained from participants who were willing to participate. Patient information sheet was provided to the participants, which explained about assessment and treatments involved in the study. Subjects were assessed in detail on the day of referral for physiotherapy following their consent; those who satisfy the inclusion criteria were recruited. Subjects were allotted to either control group (conventional physiotherapy) or experimental group (physiotherapy including resistance exercises) on alternate sequence.

Fig 2. Flow chart of recruitment as shown below

Participants were assessed in detail including demographic data, history, date of surgery, type of surgery, approach of incision, visual analogue scale (VAS), swelling, spasm, tenderness, range of motion, strength (MMT), limb length measurement and girth measurement.

Control group received conventional treatment from the day patient was referred for physiotherapy till the day of discharge. (Details below)

Physiotherapy treatment protocol for control group

Bedside exercises (before drain removed)

  Quadriceps sets

  Gluteal sets

  Ankle pump

Progress to following exercises after drain removed in addition to above i.e.

  Heel slides

  Passive/active assisted hip abduction progress to active hip abduction in supine position

  Terminal knee extension

  High sitting knee flexion extension

  Gait training with weight bearing as tolerated (on recommendation of surgeon on based on cemented vs. non-cemented) and progressing to cane or independent ambulation

The above-mentioned exercise will be performed with using precaution as below:

·   Avoid hip flexion >900

  Avoid adduction and internal rotation beyond neutral

Advice will be given for taking precaution in ADL

  Transfer the sound side from bed to chair or chair to bed.

  Do not cross the leg

  Keep the knees slightly lower than the hips when sitting

  Avoid sitting in low soft chair

  Use a raised toilet seat

  Avoid bending the trunk over the legs when rising from and sitting down in a chair

  When ascending the stairs, lead with the sound leg. When descending leading with the operated limb

  Pivot on sound lower extremity

  Avoid standing activities that involve rotating the body toward the operated extremity

Experimental group received same treatment as control group with additional isometric hip abductor strengthening exercise (within the tolerance) as additional treatment post removal of drain (as seen in Fig 3) till the day of discharge.

Fig 3. Isometric hip abductor strengthening exercise

Outcome measures

1.   Visual analogue scale (VAS)

2.   Strength of abductor was taken with sphygmomanometer – procedure as described below (Fig 4)

3.   Harris hip score (HHS)

Fig 4. Strength of abductor was taken with Sphygmomanometer

All outcomes were taken at the 3rd POD and at the 8th POD.

Hip muscle strength test methodology

  The sphygmomanometer was used for conducting the strength test, the instrument was first inflated to register 20 mm of mercury and the therapist placed patient’s left or right hand inside the cuff, depending on which limb and movement was being tested

  The valve of the Sphygmomanometer remained closed to prevent any release of air

  Hold test was used for recording the strength values

  After each test, the pressure within the cuff was totally released and the procedure was repeated from the first step. 3 trials were conducted.

Procedure

  The test for hip abduction (Fig 4) was conducted with the subject in supine position.

  In order to test the left leg, the therapist stood left side of the subject, with the subject's leg in neutral position.

  The therapist, having placed the cuff on the right hand and positioned it on just above the knee lateral side.

  The test was started by asking the patient to move his leg outside by pushing the therapist hand and asked the patient put his maximum effort. Therapist resisted this action with maintaining the same position and not allowing the patient to do abduction. The maximum pressure exerted on the cuff was then recorded and the subject was asked to relax for 30-35 seconds before the second test was performed.

The maximum effort of the three trials was recorded. The actual effort was (maximum of three) ­ 20 mm of Hg.

Statistical analysis

1.   All statistical analyses were performed with SPSS (Statistical Package for Social Science) version16 software.

2.   Descriptive statistics including Mean, Standard Deviation (SD) and Standard Error Mean (SEM) were calculated.

3.   Independent t test was applied to compare inter group comparison by Mean values, Standard Deviation, Standard Error of Mean and P – value.

4.   Paired t test was applied to compare intra group comparison in Mean values, Standard Deviation, Standard Error of Mean and p value.

5.   One sample t test was applied to compare mean strength of normal and mean strength of operated limb.

Results

Total patients with hip replacement were 18 (03 excluded). Total number of the hip operated cases were 15 (11 patients were following fracture and 4 were with AVN). In experimental group total no. was 8 and in control group total no. was 7. Age ranged from 40 to 83 years. 9 were cemented and 6 were un-cemented. 13 patients were operated with postero-lateral approach and 2 with lateral approach.

Table 1: Comparison of baseline characteristics of two groups on the 3rd POD

 

Group

N

Mean

SD

SEM

p

Age (years)

Experimental

8

57.88

7.18

2.54

0.821

Control

7

59.43

17.44

6.59

VAS 3rd POD

Experimental

8

2.78

0.43

0.15

0.941

Control

7

2.80

0.83

0.31

Strength (mm Hg) 3rd POD

Experimental

8

33.25

4.40

1.56

0.22

Control

7

30.29

4.54

1.71

HSS 3rd POD

Experimental

8

52.38

4.17

1.48

0.061

Control

7

46.57

6.66

2.52

 

Table 2: Comparison of mean strength of both experimental and control group on the 3rd POD with mean strength of normal

Strength (mm Hg) 3rd POD

N

Mean

SD

SEM

p

Experimental

8

33.25

4.40

1.56

<0.001

Control

7

30.29

4.54

1.71

<0.001

Normal value = 101.4 mm Hg

 

Table 3: Comparison of mean difference in strength and HHS in the control group between 3rd and 8th POD

Difference between 3rd and 8th POD

Mean difference

SD

SEM

p

Strength (mm Hg)

Control

-14.57

3.59

1.36

<0.001

HHS

-21.71

7.16

2.71

<0.001

Strength (mm Hg)

Experimental

-21.00

5.13

1.81

<0.001

HHS

-22.87

4.12

1.46

<0.001

 

Table 4: Comparison of mean strength and HHS and difference of mean strength and HHS between the two groups

 

 

Group

N

Mean

SD

SEM

p

Strength

8th POD

Experimental

8

54.25

9.22

3.26

0.057

Control

7

44.86

7.99

3.02

Difference between 3rd and 8th POD

Experimental

8

21.00

5.13

1.81

0.016

Control

7

14.57

3.60

1.36

HHS

8th POD

Experimental

8

75.25

2.19

0.77

0.058

Control

7

68.29

9.23

3.50

Difference between 3rd and 8th POD

Experimental

8

22.88

4.12

1.46

0.702

Control

7

21.71

7.16

2.70

 

Discussion

The present study was planned to see the effects of resisted hip abductors given in the initial phase following THA. Routinely the patient is mobilized soon post operatively i.e. on the 3rd day and thus the structured resisted hip program many a times may be overlooked.

A number of studies have been done to evaluate the effect of hip muscles strengthening following THA15,20,22,25,26, as the approach that the surgeon takes invariably involves the abductors directly or indirectly and also as number of studies which have followed up these cases up to 2 years or more have reported the hip muscles and knee muscles to remain weak compared to the contra lateral sound limb11,26. Similarly, Fukumoto et al (2013) also reported that although hip and knee muscles strength improved considerably 6 months post THA on the involved side, the hip abductors always remained significantly below the level when compared to the healthy group20.

The present study used the sphygmomanometer (aneroid manometer) to assess the strength. The norms were prior established by the same method in the age matched normal population (mean age 51.6±7.03) in 30 subjects (60 hips), the average strength was noted as 101.4±12.80 mm of Hg. A number of studies have been done to assess the validity and reliability of use of Modified Sphygmomanometer (MoS). All the studies established adequate criterion related validity, test-retest and inter-rater reliabilities for the assessment of strength, for the majority of the assessed muscles27,28.

It has been reported that use of MoS easily trainable and that only one familiarization could yield reliable results and this method of assessment was not time consuming27,28.

However, Sherrington et al (2005) investigated the test-retest reliability of various tools viz. measures of strength, balance, gait and functional performance in older people following hip fracture. With regards to Sphygmomanometer the author sounds caution as it was found to have a curvilinear relation with hand held dynamometer i.e. did not provide comparable measurement throughout the range29.

13 of 15 subjects in present study were with postero-lateral approach with reconstruction of the posterior aspect. Reconstruction of posterior capsule, piriformis tendon and external rotators has been reported to be enhancing the stability of primary THA6,10. Two of the cases in the present study were with lateral approach.

Number of studies reported no significant difference in hip abductor strength recovery and other outcomes between the two approaches i.e. lateral and posterlateral8,9,24. The study durations of follow ups were different. One study followed up at 3 months and at 1 year8, other followed up at the end of one year9, third study assessed at the end of 2 years24. The outcome measures used few of them i.e. pain, hip abductor strength, Trendelenburg test, HHS, etc.

The strength of hip abductor muscle on the 3rd day post-operative compared to normal was significantly reduced in both the groups (Table 2). As seen the reduction in strength post-operative was almost 70%. Early loss of the strength in the muscles close to the operated hip joint is referred to as ‘arthrogenic muscle inhibition’ i.e. inhibition from CNS to activate muscles due to intra articular swelling, inflammation, pain and joint laxity. Overtime this leads to muscle atrophy14.

In the present study the experimental group received manual isometric strengthening for the hip in addition to the conventional physiotherapy. The hip abductor strength was assessed in both the experimental and control group. Within each group significant improvement in strength was seen on the 8th post-op day (Table 3). It is similarly reported that early rehabilitation with either standard physiotherapy and standard physiotherapy with isometric exercise program both show improvement25, also that as the days progress post operatively the weakness becomes less pronounced at the end of the week14,25.

In the initial comparison not only is the strength improved on the 8th day as compared to 3rd post-op day, also the HHS shows improvement within each group, i.e. <70 (poor) to 70-80 (fair) on the 8th day. This was so except in one case in the control group who was with bilateral AVN, also with uncemented THA and therefore immobilized, in the present study. In HHS mainly, the change was in the scoring of pain with analgesics ongoing and also there was improvement in the distance walked and ability to climb stairs.

Inter group comparisons, analysing mean difference in strength, showed experiment group to be significantly better compared to the control / conventional therapy group. This is in agreement to a number of studies comparing the same although at similar and / or at different intervals post operatively15,20,22,25,26.

Early rehabilitation with either standard physiotherapy and standard physiotherapy with isometric exercise program both show improvement with experimental group showing better progress than the control group treated with standard protocol25.

Similarly, Husby et al (2009) studied the comparison between the strength training group and conventional PT group following THA at 1st week and 5th week. Both the groups were given physiotherapy for 3-5 times per week for four weeks. Both were similar on the assessment at 1st week but at 5th week, the group that had received resisted strength training in the first week was significantly better in strength, work patterns, gait and QOL compared to the conventional PT group15.

The same author (2010) also reports that at 6-12 months follow up too, the group that received maximal strength training early postoperative along with the conventional PT showed significantly better work efficiency compared to only conventional PT. However, the author emphasises that prolonged strength and endurance training is required to be continued for full recovery in the patients following THA22.

Rasch et al (2010) studied elderly patients before THA and at 6 months and at 2 years post-surgery. These patients post operatively had 10 sessions of weekly group training after operation and were then put on home program. At the follow ups the compliance amongst them varied ranging from no exercises to exercising several times per week.  The patients showed weakness persisting in the hip muscles compared to contra lateral sound limb, which was more at the end of 2 years as compared to the 6 months assessment, although gait and balance had recovered. To prevent the weakness of the hip muscles the authors’ recommended intense program targeting hip abductor strengthening26.

Hip extensor and flexor strength and endurance is important following THA to avoid post-op limping as impaired muscle strength, endurance in these muscles, and limping severity were strongly associated postoperatively than preoperatively18. Similarly, Fukumoto et al also reported (2013) that although hip and knee muscles strength improved considerably 6 months post THA on the involved side, the hip abductors always remained significantly below the level when compared to the healthy group20.

Late phase rehabilitation following THA has also been found to be associated with significant improvements in muscle strength, postural stability, and self-perceived function in patients 4 to 12 months after THA19.

Conclusion

The study concludes:

1.   Early phase rehabilitation within the groups, in both experiment and control showed significant improvement in strength and HHS.

2.   Mean difference of strength comparison between groups showed experiment group to be significantly better than the control, HHS showed no significant difference.

The present study therefore concludes that resisted hip muscles exercises must be started early in the phase of rehabilitation and based on the reports from the literature be continued for maintenance.

Scope of further studies will be able to convincingly prove the lasting effects and / or requirement of continuous Rehabilitation measures with periodic regular follow ups.

Acknowledgement: The authors are grateful to the Sumandeep Vidyapeeth, a deemed university for all the support provided.

Conflict of interest: None

References

1.    van Egmond PW, Taminiau AH, van der Heide HJ. Hemiarthroplasties in young patients with osteonecrosis or a tumour of the proximal femur; an observational cohort study. BMC Musculoskelet Disord. 2013 Jan 17; 14:31. PMID: 23327536 DOI: 10.1186/1471-2474-14-31

2.    Shan L, Shan B, Graham D, Saxena A. Total hip replacement: a systematic review and meta-analysis on mid-term quality of life. Osteoarthritis Cartilage. 2014 Mar; 22(3):389-406. PMID: 24389057 DOI: 10.1016/j.joca.2013.12.006

3.    Pachore JA, Vaidya SV, Thakkar CJ, Bhalodia HK, Wakankar HM. ISHKS joint registry: A preliminary report. Indian J Orthop. 2013 Sep; 47(5):505-9. PMID: 24133312 DOI: 10.4103/0019-5413.118208

4.    Haveri SM, Uppin RB. Results of uncemented total hip replacement done in very young patients. Int Surg J. 2014 Aug; 1(2):80-3. DOI: 10.5455/2349-2902.isj20140811

5.    Edmunds CT, Boscainos PJ. Effect of surgical approach for total hip replacement on hip function using Harris Hip scores and Trendelenburg’s test. A retrospective analysis. Surgeon. 2011 Jun; 9(3):124-9. PMID: 21550516 DOI: 10.1016/j.surge.2010.08.014

6.    Masonis JL, Bourne RB. Surgical approach, abductor function, and total hip arthroplasty dislocation. Clin Orthop Relat Res. 2002; 405:46-53. DOI: 10.1097/01.blo.0000038476.05771.6c

7.    Queen RM, Appleton JS, Butler RJ, Newman ET, Kelley SS, Attarian DE, Bolognesi MP. Total hip arthroplasty surgical approach does not alter postoperative gait mechanics one year after surgery. PM R. 2014 Mar; 6(3):221-6. PMID: 24056161 DOI: 10.1016/j.pmrj.2013.09.006

8.    Downing ND, Clark DI, Hutchinson JW, Colclough K, Howard PW. Hip abductor strength following total hip arthroplasty: a prospective comparison of the posterior and lateral approach in 100 patients. Acta Orthop Scand. 2001 Jun; 72(3):215-20. PMID: 11480593 DOI: 10.1080/00016470152846501

9.    Sayed-Noor AS, Hanas A, Sköldenberg OG, Mukka SS. Abductor muscle function and trochanteric tenderness after hemiarthroplasty for femoral neck fracture. J Orthop Trauma. 2016 Jun; 30(6):e194-200. PMID: 27206260 DOI: 10.1097/BOT.0000000000000532

10.  Tarasevicius S, Robertsson O, Wingstrand H. Posterior soft tissue repair in total hip arthroplasty: a randomized controlled trial. Orthopedics. 2010 Dec; 33(12):871. PMID: 21162508 DOI: 10.3928/01477447-20101021-11

11.  Judd DL, Dennis DA, Thomas AC, Wolfe P, Dayton MR, Stevens-Lapsley JE. Muscle strength and functional recovery during the first year after THA. Clin Orthop Relat Res. 2014; 472(2):654-64. PMID: 23817756 DOI: 10.1007/s11999-013-3136-y

12.  Jensen C, Aagaard P, Overgaard S. Recovery in mechanical muscle strength following resurfacing vs standard total hip arthroplasty – a randomised clinical trial. Osteoarthritis Cartilage. 2011 Sep; 19(9):1108-16. PMID: 21749928 DOI: 10.1016/j.joca.2011.06.011

13.  Steinhilber B, Haupt G, Miller R, Boeer J, Grau S, Janssen P, Krauss I. Feasibility and efficacy of an 8-week progressive home-based strengthening exercise program in patients with osteoarthritis of the hip and/or total hip joint replacement: a preliminary trial. Clin Rheumatol. 2012; 31(3):511-9. PMID: 22086491 DOI: 10.1007/s10067-011-1893-0

14.  Holm B, Thorborg K, Husted H, Kehlet H, Bandholm T. Surgery-induced changes and early recovery of hip-muscle strength, leg-press power, and functional performance after fast-track total hip arthroplasty: a prospective cohort study. PLoS One. 2013 Apr; 8(4):e62109. PMID: 23614020 DOI: 10.1371/journal.pone.0062109

15.  Husby VS, Helgerud J, Bjørgen S, Husby OS, Benum P, Hoff J. Early maximal strength training is an efficient treatment for patients operated with total hip arthroplasty. Arch Phys Med Rehabil. 2009 Oct; 90(10):1658-67. PMID: 19801053 DOI: 10.1016/j.apmr.2009.04.018

16.  Foucher KC, Hurwitz DE, Wimmer MA. Preoperative gait adaptations persist one year after surgery in clinically well-functioning total hip replacement patients. J Biomech. 2007; 40(15):3432-7. PMID: 17644101 DOI: 10.1016/j.jbiomech.2007.05.020

17.  Jan MH, Hung JY, Lin JC, Wang SF, Liu TK, Tang PF. Effects of a home program on strength, walking speed, and function after total hip replacement. Arch Phys Med Rehabil. 2004 Dec; 85(12):1943-51. PMID: 15605331

18.  Horstmann T, Listringhaus R, Brauner T, Grau S, Mündermann A. Minimizing preoperative and postoperative limping in patients after total hip arthroplasty. Am J Phys Med Rehabil. 2013 Dec; 92(12):1060-9. PMID: 23739275 DOI: 10.1097/PHM.0b013e3182970fc4

19.  Trudelle-Jackson E, Smith SS. Effects of a late-phase exercise program after total hip arthroplasty: a randomized controlled trial. Arch Phys Med Rehabil. 2004 Jul; 85(7):1056-62. PMID: 15241750

20.  Fukumoto Y, Ohata K, Tsukagoshi R, Kawanabe K, Akiyama H, Mata T, Kimura M, Ichihashi N. Changes in hip and knee muscle strength in patients following total hip arthroplasty. J Jpn Phys Ther Assoc. 2013; 16(1):22-7. PMID: 25792900 DOI: 10.1298/jjpta.Vol16_002

21.  Müller M, Tohtz S, Winkler T, Dewey M, Springer I, Perka C. MRI findings of gluteus minimus muscle damage in primary total hip arthroplasty and the influence on clinical outcome. Arch Orthop Trauma Surg. 2010 Jul; 130(7):927-35. PMID: 20221834 DOI: 10.1007/s00402-010-1085-4

22.  Husby VS, Helgerud J, Bjørgen S, Husby OS, Benum P, Hoff J. Early postoperative maximal strength training improves work efficiency 6-12 months after osteoarthritis-induced total hip arthroplasty in patients younger than 60 years. Am J Phys Med Rehabil. 2010 Apr; 89(4):304-14. PMID: 20134307 DOI: 10.1097/PHM.0b013e3181cf5623

23.  Jogi P, Overend TJ, Spaulding SJ, Zecevic A, Kramer JF. Effectiveness of balance exercises in the acute post-operative phase following total hip and knee arthroplasty: A randomized clinical trial. SAGE Open Med. 2015 Feb 11; 3: 2050312115570769. PMID: 26770765 DOI: 10.1177/2050312115570769

24.  Kiyama T, Naito M, Shinoda T, Maeyama A. Hip abductor strengths after total hip arthroplasty via the lateral and posterolateral approaches. J Arthroplasty. 2010 Jan; 25(1):76-80. PMID: 19359133 DOI: 10.1016/j.arth.2008.11.001

25.  Temfemo A, Doutrellot PL, Ahmaidi S. Early muscular strengthening after total hip arthroplasty: association of two models of rehabilitation. Ann Readapt Med Phys. 2008 Jan; 51(1):38-45. PMID: 18164092 DOI: 10.1016/j.annrmp.2007.09.008 [Article in French]

26.  Rasch A, Dalén N, Berg HE. Muscle strength, gait, and balance in 20 patients with hip osteoarthritis followed for 2 years after THA. Acta Orthop. 2010 Apr; 81(2):183-8. PMID: 20367414 DOI: 10.3109/17453671003793204

27.  Souza LA, Martins JC, Moura JB, Teixeira-Salmela LF, De Paula FV, Faria CD. Assessment of muscular strength with the modified sphygmomanometer test: what is the best method and source of outcome values? Braz J Phys Ther. 2014 Mar-Apr; 18(2):191-200. PMID: 24839045

28.  Souza LA, Martins JC, Teixeira-Salmela LF, Lara EM, Moura JB, Aguiar LT, de Morais Faria CD. Validity and reliability of the modified sphygmomanometer test to assess strength of the lower limbs and trunk muscles after stroke. J Rehabil Med. 2014 Jul; 46(7):620-8. PMID: 24849895 DOI: 10.2340/16501977-1823

29.  Sherrington C, Lord SR. Reliability of simple portable tests of physical performance in older people after hip fracture. Clin Rehabil. 2005 Aug; 19(5):496-504. PMID: 16119405 DOI: 10.1191/0269215505cr833oa

30.  Brokelman RB, Haverkamp D, van Loon C, Hol A, van Kampen A, Veth R. The validation of the visual analogue scale for patient satisfaction after total hip arthroplasty. Eur Orthop Traumatol. 2012 Jun; 3(2):101-5. PMID: 22798966 DOI: 10.1007/s12570-012-0100-3