Advancing Precision in Penile Length Measurement: Evidence-based Synthesis of Stretched Penile Length INdicator Technique (SPLINT)

ABSTRACT

Purpose:

The purpose of this study was to synthesize evidence and propose a technique for estimation of stretched penile length (SPL) applicable to children.

Materials and Methods:

This review has been conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses. PubMed, Embase, and Scopus databases were queried on penile length (PL) measurement techniques in humans published from 1990 onward. The devices and the techniques used for PL measurement, state of the penis, the habitus of the participants, proximal and distal landmarks for measurement, handling the foreskin and pubic pad of fat, optimal stretching of the penis, and other factors (including the environment) which should be accounted for in the technique were identified from the study cohort (90895 participants across 145 included studies).

Results:

PL has been represented through flaccid (33.79%), stretched (81.3%), and erect (12.41%) PLs as well as the greatest corporeal length (1.4%). Following devices have been used to measure the PL in the study cohort: rulers [54.68%], calipers [9.7%], measuring tapes [14.5%], coloured measuring strips [2.06%], spatulas/tongue depressors [11.03%], FitKit, syringe [1.4%], cotton swab (and ruler), titan cylinders, slide gauge and ultrasonography [1.37%]. The factors relevant to SPL measurement have been incorporated into the proposed SPL INdicator Technique (SPLINT) which is essentially a holistic extension of the “Conventional PL Measurement” technique.

Conclusions:

There is a wide range of heterogeneity in the technique for estimation of PL across the study cohort; the underlying factors have been identified along with the respective variables, and the SPLINT for SPL has been described.

INTRODUCTION

Over the centuries, penile size has been equated with power, virility, masculinity, and social status.[1] The size of the penis has intrigued mankind if not the entire humankind as much as it has plagued the minds of many since antiquity. An Internet survey across 50,000 heterosexual individuals found that only a little more than one-half of men were satisfied with their respective penile sizes.[2] The pediatric surgeons (and pediatricians) are often confronted with curious parents whose kids have been treated for genital aberrations such as hypospadias, epispadias, buried penis, micropenis, obesity, or congenital short urethra. The concerns may sometimes be related to false impressions gained from peer discussions, sexually explicit media content, and advertisements of penile length (PL) augmentation products. The social and interpersonal lives of the affected individuals are at stake. The measurement of PL and a comparison against the acceptable standard becomes mandatory to resolve such situations.

In the absence of a consensus statement, assessment of the PL is associated with several methodological challenges such as the state of the penis (flaccid, erect, or stretched),[3,4,5,6] the proximal or distal landmarks for measurement, and the measuring device.[7,8] The current review has been designed and conducted to evaluate the diverse techniques of PL measurement and describe an evidence-based optimal approach to estimation of PL in children.

MATERIALS AND METHODS

This review has been conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines[9] [Figure 1a and b]. The study methods were outlined in advance, and databases (PubMed, Embase, and Scopus) were queried for primary research (1990 onward) on the methodology of PL measurement. Although the primary focus has been to describe a technique applicable to children primarily, no age restriction was imposed in the search strategy; any factor considered relevant to PL measurement (children or adults) has been scrutinized.

Figure 1.

(a) Preferred Reporting Items for Systematic Reviews and meta-analyses flow diagram (b) material and methods

The synthesis is representative of 145 studies from across the globe representing all 7 continents [Figure 2].[3,4,5,6]

Figure 2.

Geographical distribution of studies included in the study cohort

RESULTS

The study cohort comprised 90,895 cases across 145 studies;[3,4,5,6,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,88,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127,128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,144,145,146,147,148,149,150] the participants varied in age from neonates to 98 years. The study characteristics are tabulated in Table 1.

Table 1.

Characteristics of studies describing the penile length measurement included in the study cohort

Theme of Study	No. of Studies/No. of participants
• Generation of normative data	72/n=78,169
• Different aspects of hypospadias	22/n=2682
• Penile Length in different conditions cryptorchidism, obesity, buried penis, prostate cancer, phthalate exposure, Peyronie’s disease and erectile dysfunction	24/n=5404
• Comparison of penile length in different states [37,123,134,143] flaccid or erect	4/n=620
• Different techniques of penile length measurement[6,25]	2/n=356
• Consultations for small penis [54,94,118,125,131]	5/n=480
• Correlation of penile size with other body dimensions	7/n=1869
Body-mass index,[81] nose,[20] anogenital distance,[56,61] length of index finger,[66,112] second-to-fourth digit ratio,[49,90] waist to hip ratio,[66,112] gluteal size,[117] length of the left foot (tip of thumb to end of the heel) (7 of 145; 4.82%),[5] shoe size[126]
• Condoms[106,141,145]	3/n=1125
• Interventions for penile length [18,60,97,110,111,135]	6/n=190
Study Designs in the cohort
• Case-control (n=2)	Retrospective (n=14; 9.65%)
• Cross-sectional studies (n=40; 27.58%)	Randomized controlled trials (n=12)
• Prospective (n=75; 51.72%)	Rase series/reports (n=2)
Interesting categories of participants
• Cadavers within 3 days of death[20,32]
• Doctors with an interest in andrology/penile reconstruction[31]
• Gay population[128]

The number of publications on the subject has increased consistently from 1991 to 2020 [Figure 3].

Figure 3.

The number of publications over any 5 consecutive years has increased consistently from 1991 to 2020

Across the study cohort, the PL has been represented through flaccid or nonerect PL (non-EPL): n = 49; 33.79%, stretched PL (SPL): n = 118; 81.3%, EPL (n = 18; 12.41%), and the ultrasonographic measurement of the greatest corporeal length (n = 2; 1.4%).

The proximal landmark for measurement of PL is taken as the base of the penis: pubic symphysis,[27,30,57,97] pubic bone,[38,49,60] pubopenile skin angle[67,82] or vertex,[15,62,81] penopubic junction,[23,87,132] penoscrotal junction,[40,136] scrotum,[12,83] pubopenile junction (pubic ramus),[24,35,44] pubic angle,[19] pubic arch,[21,88] lower end of pubic bone just above the suspensory ligament,[88] belly,[139] and dorsal back root.[148]

Compression of the pubic pad of fat has been identified as an independent factor in most of the studies.[42,44,49,97,143] Gabrich et al.[114] has nomenclated the PL into apparent and real lengths wherein apparent length was measured without compressing the pubic pad of fat; hence the terms apparent flaccid length, real flaccid length, apparent stretched length max and real stretched length max.

The distal landmark for measuring the PL is the tip of the penis. The prepuce is a limiting factor in identifying the tip of the glans penis (top of glans, glans extremity, distal end of glans, penile tip, and head of penis). A significant number of studies have specified that the foreskin was not included in the measurement.[44,95,119] Palpation has been used for this purpose.[29,71,129,149] However, it is not always clear how this was made possible in patients with phimosis, physiological or pathological. A couple of studies have used the urethral meatus, coronal sulcus, mid of the glans, base of glans (coronal ridge), proximal end of corona, etc., as the distal landmark. A few studies have oversimplified the description of the technique: pubic ramus to the glans.[50]

The accurate correlation of the tip of the glans with the corresponding reading on the measuring device (parallax error) has not been discussed in most of the papers; a few authors have, however, held another device perpendicular to the measuring device to accurately identify the tip of the glans.[61,113]

The length of the penis has been measured along its dorsal (at least 55 of 145 studies; 37.9%) or ventral[105,136] aspect. Multiple papers have not specified the laterality of measurement.[59,60,66,68,130]

SPL correlates with the EPL.[136,143,151] However, such measurements must be performed in awake conditions since general anesthesia eliminates the pain and discomfort associated with stretching.[5] The magnitude/endpoint of stretching the penis includes the point of increased resistance,[11,26,51,146] maximal manual traction,[82,110,111] gentle painless extension,[88] fully or maximally stretched,[92] or maximal but not painful extension.[81] The traction should be gentle and sustained.[28] Repeated manual stretching of the penis for three times has been suggested.[143] The use of a spring scale has been described to ensure uniform stretching force (450 g).[93]

Self-reported measurements have been accepted.[15,46,70,101,106,128,138,141,144]

The preferred environment has been described across multiple studies. Fifty-two (of 145) studies have reported the room temperature: 20°C–25°C (n = 8)[10,58,92] or specific values such as 21°C (n = 2)[6,58] and > 22°C (n = 4).[38,68] Three studies have reported the environmental temperature to be 36°C–40°C. Li et al. described that the measurements of PL have been described in a semi-obscured room,[100] examination room,[38,68] air-conditioned medical consulting room,[15,42,81] quiet, isolated comfortable & climate-controlled room,[37] warm & comfortable room temperature,[11] stable room with comfortable temperature,[19] normal temperature in quiet state,[48] warm environmental conditions[51,71] and out-patient clinic.[10] No mention of the environment was found in at least 67 studies. The presence of another family member or parents or legal guardians has been mentioned.[25,26,35,36,50,64,65,92]

Measurements were performed in the preoperative holding area before the administration of any anesthetic medicine,[121,129] immediately before surgery after administering local anesthesia,[76] inside the operating room during induction,[5] or under general anesthesia.[12,88] Majority of the studies have performed the measurements while the patient was awake (at least 125 of 145 studies). Ikegaya et al. and Suzuki et al. have performed measurements on cadavers.[20,32] Aslan et al. have specified that the measurements were conducted under ambient light,[36,89] dimly lighting,[93,135] room lighting,[126] or sufficient light.[39] Aslan et al. have performed all measurements between 10:00 AM and 4:00 PM.[89]

The penile measurements were conducted in privacy with warm examining hands and recorded.[54] The use of disposable latex gloves at the time of measurement has been described.[114] Penile measurement promptly after undressing prevents the effects of touch and temperature.[17,49,54,90,101,104,124,150] Cadaver-based measurements were conducted in a supine position with the penis held perpendicular to the long axis of the body.[20,32]

Other parameters pertaining to penile dimensions observed in the study cohort include the penile width,[22,28,77] penile circumference,[16,109] dorsal glans length,[4] ventral glans length,[4] glans width,[4] unaroused glans diameter,[17] testicular volume,[33,48] and the various anogenital distances.[28]

Measuring device used

The device used to measure the PL has been specified in 131 (of 145; 90.34%) articles and is summarized in Table 2.

Table 2.

Devices used for measurement of penile length

* Rulers of different types[10,43,58,68],	* Fitkit[70,106],
* Calipers[12,77,63,87],	* Syringe[138],
* Measuring tapes[66,69,120],	* Cotton swab (and ruler)[142],
* Colored measuring strips[128,145],	* Titan cylinders[60],
* Spatulas[28,55,75],	* Slide gauge (Baty International, Burgess Hill, West Sussex, UK)[116],
* Tongue depressors[61,113],	* Ultrasonograph[144,150]
Ruler	Calipers
* Most commonly used (n=76; 54.68%)	Described in at least 14 studies (n=14 of 145; 9.7%); cumulative sample size: 2470.
Different types (specified in 44/76; 57.9%)	* Conventional (or unspecified) vernier: 9 studies (9 of 14; 874 participants)
* Rigid ruler made of steel (4 of 76)[114,123],	* Digital vernier: 5 studies (5 of 14; 1596 participants)
* Wood (1 of 760 or or plastic (9 of 76)[48,140],	* Freeze frame electronic screen caliper for the fetal penis measurements (sample size n=94)[83]
* Semi-rigid or flexible rulers and paper rulers (10 of 76)[99,121]
Rounding-off criteria for the observed readings:	* Slide gauge (Baty International, Burgess Hill, WestSusex, UK) for flaccid PL[116] (possibly a modified version of the Vernier calipers).
* Specified in at least 19 studies
** Nearest 0.5 cm (n=10)[120], even 2 mm (n=l)[95], 1 mm (n=6)[81,128], 0.5 mm[59] and to the nearest quarter inch[139].
Wooden spatulas or Tongue Depressors	Syringe
Described in 16 studies (n=16 of 145; 11.03%): cumulative sample size: 11155 (of 90895; 12.27%)	Described in 2 studies (n=2 of 145; 1.4%)[105,138]: cumulative sample: 198 (of 90895; 0.22%).
* Mark was made on the spatula at the level of the tip of the glans penis	* The needle-bearing end is cut transversely and the piston is introduced through this end.
* Value (cm) was read using a second measuring device such as the	The edge with the flange is used to introduce the penis into the syringe which is pressed
* measuring tape (n=5 of 145; 3.44)[11,26,44,129,137]	against the pubis (to exclude the prepubic fat).
* ruler (n=2 of 145; 1.37%)[51,92]	* The piston is withdrawn to create a suction within.
* electronic digital sliding caliper (n=l of 145; 0.68%)[28]	* The length of the penis is taken from the scale on the barrel when the suction is optimal
* digital caliper (n=l of 145; 0.68%)[98].	(the definition of optimal is obscure).
Measuring Tape	FiTKit
Described in 21 studies (n=21 of 145; 14.5%): cumulative sample size: 15820 participants (of 90895; 17.4%).	Described in 2 studies (n=2 of 145; 1.4%)[70,106]: cumulative sample: 2481 (of 90895;
	2.72%).
	* Simple device to identify the perfect condom size[153].
Ultrasound in conjunction with other measuring devices (ruler and wooden spatula) for corporeal length	Uncalibrated colour-coded measuring strips
	Described in three studies (of 145; 2.06%); cumulative sample size: 617 (of 90895; 0.67%)
Described in two studies (of 145; 1.37%), cumulative sample size: 166 participants (out of 90895; 0.18%)[144,150].	* Erect penile length measured by the participant himself (or the respective partner) [128,141,145].
* Smith et al[144]: measured the SPL (ruler); greatest corporeal body length: longitudinal ultrasound (participant supine with legs flat and adducted) on the dorsum of the flaccid	* The strips were subsequently measured for the PL.
penis with a 7.5 MHz linear transducer probe	Cotton Swab
* Crural and pendulous parts of the corpora were included in a single oblique parasagittal	Described by Mureau in 60 patients of hypospadias 9-18 years of age
plane of section.	Cotton swab was held against the dorsum of the stretched penis; the length of the swab was then confirmed with a ruler[142].
* Khairil et al[150] measured the corpora with the scan plane tilted slightly caudad to improve visualization of the crus posterior to the pubic arch.
* Length of the posterior crus from its termination at the inferior border of the pubic arch to the suspensory ligament was measured followed by the length from the suspensory ligament to the round conical anterior termination of the corpus.	Titanium Cylinders
	Titan cylinders with minimized rear tip extenders (RTEs) estimate the effect of implant cycling on the PL: described in 40 patients[60].

Schonfeld and Beebe[152] described the technique of PL measurement way back in 1942; the same technique (conventional SPL measurement; CPLM) has been referenced by at least six studies (6 of 145; 4.13%) in the cohort.[26,51,75,105,129,138] These studies have cumulatively measured the PL in 4485 (of 90895; 4.93%) participants. Ozbey et al.[138] have, in addition, compared the measurement of PL with the syringe against the Schonfeld and Beebe technique[152] as gold standard. The syringe methods have been held superior on the pretext of technical simplicity, lesser inter-observer variations, and reproducibility.[138]

Position of the patient at the time of measurement

Position of the patient at the time of measurement has been reported in 57 studies (of 145; 39.3%): supine or dorsal decubitus (n = 50 of 57; 87.71%) or standing with the penis held parallel to the floor (6 of 57; 10.52%).[6,17,30,49,66,89] Roy et al.[33] measured the SPL of children in a standing position and neonates in a supine position.

Intra-observer and inter-observer variability

Most of the authors have relied on single (or unspecified number of) measurement (n = 91); an average of 2[75,116,126,137] or 3[131] readings have been considered appropriate by 33 and 21 authors, respectively. Several studies have relied upon single measurements; some of they have described pre-study training of the observers,[24,44,76] others have ensured that a single observer takes the entire measurements across the cohort[61,62,81,104,136] while others have documented negligible intra-[77,83,98,100] or inter-observer variations.[33,72,75,97,99] The inter-observer bias has been estimated to be acceptable (negligible).[72,83,97,99,100,112,113,115,129,137] Roy et al. have documented that maximal inter-observer bias was 2 mm and that the mean of the two values was recorded[33] while Boas et al. have documented that 95% of the paired measurements (two different observers) were within ± 0.67 cm while the intra-observer variation was 0.18 cm.[116] Al Herbish has calculated the intra-observer (repeating measurement on the same subject by the same examiner) and inter-observer (repeating measurements on the same subject by different examiners) variations in 10% of the study participants.[129]

DISCUSSION

The heterogeneity observed across the study cohort is multi-contextual and pertains to the type of PL, the proximal and distal landmarks for measurement, the device used, and the description of environmental or other factors. Due to the lack of universally acceptable protocols, technical complexities in the measurement of PL, and the multitude of confounding factors, it is nearly impossible to draw robust conclusions on the different aspects of PL measurement. Consequently, the consensus on such an important dimension of “mankind” is obscure. However, it was possible to draw a list of factors and conditions which indispensably “pillar” the description of any technique for measurement of PL [Table 3]. Individual studies have focused on a unique combination of factors from this list.

Table 3.

Factors relevant while describing the technique used for penile length measurement

✓	Environment: room temperature,[11,19,48] lighting ,[36,93,126] privacy,[33,54] patient comfort,[43,71] presence or absence of guardian (s)/parents [26,35,50,64], number of observers [75,116,131].
✓	State of the participant: awake,[109,115,120] sedated, under general anesthesia.[12,88] The stretched penile length measured under general anesthesia is likely to be different from that measured in awake condition since the patient will not sense pain or discomfort associated with stretching.[5]
✓	Position of the participant: supine[20,32,144] or standing.[6,17,30]
✓	Time from undressing to actual measurement may affect the penile dimensions due to the effect of environment, tactile, and other stimuli.[49,54,90]
✓	Description of the measuring device: unambiguous description of the measuring device should be provided.
✓	Which penile length is being measured: flaccid penile length, stretched penile length and erect penile length?
✓	The proximal landmark of measurement and their identification: usually the peno-pubic skin junction at the root of the penis.[23,87,132,136]
✓	The distal landmark of measurement and their identification: the tip of glans,[5,10,18] mid-glans,[46,146] the tip of meatus,[111,122,134] the corona,[68,99,127] etc.
✓	Number of hands (observers) involved with the technique (measurement)
✓	Pubic pad of fat may be compressed to eliminate the effect of obesity [differentiate b/w real and apparent lengths.[42,44,49,97]
✓	Handling of the foreskin: the volume of the foreskin is variable needs to be eliminated from measurement in uncircumcised participants[44,95,119]
✓	Degree of stretching of the penis (for SPL) should be uniform, the upper limit of stretching should be specified: such as upto the point of increase in resistance,[11,26,51,146] pain & discomfort,[94,123] maximal manual stretching[82,110,111] or use of spring scale.[93]
✓	Number of observers taking the measurement/their training or experience: Estimation of the intra-observer[77,83,98] and inter-observer[33,72,75,99] variations.
✓	Calibration of the measurement device[59,81] and rounding off[58,109,120] must be described.
✓	The modalities used for achieving an erection and the optimal degree of erection considered appropriate for recording the dimensions must be described.[58,128,141,145]
✓	Zero error: Usually all rulers will have a few mm of uncalibrated length before the zero; this must be accommodated in the observed readings.

The length of the flaccid penis is highly variable and sensitive to environmental and body temperature, tactile or other physical stimuli, stress and anxiety, psycho-emotional state of mind including arousal and circadian rhythms, hydration and blood volume, recent intake of specific pharmacological agents, duration since last orgasm, other environmental factors, etc.

The true physiological or functional length of the penis is the PL at the time of erection. The natural erection which happens at the time of sexual arousal or activity may not be completely replicable with manual or therapeutic stimulation. The measurement is more relevant for conditions relating to sexual function and performance. This may not be feasible for all patients at all times and across all age groups.

The SPL is considered the “gold standard” for measurement and comparison of PL.[144,150] SPL provides a baseline measurement of the potential length of the penis when erect.[5,136,142,153] The measure is more relevant from the perspective of pediatric patients including those with urological malformations. The SPL will, however, be affected by a variety of factors intrinsic to the patient such as the elasticity of the penile tissues, inter-individual variability, psychological factors, hydration, and temperature. While there is a general correlation between the SPL and the EPL, SPL may not be a precise indicator of the EPL. The SPL is typically somewhat shorter than EPL since it does not account for the additional expansion which occurs during engorgement.

The current synthesis has identified the factors which must be considered during PL measurement [Table 3]. Based upon these observations, the study group has compiled the essential components into a model technique for the measurement of SPL (hereafter referred to as the SPL INdicator Technique [SPLINT]).[Figure 4] SPLINT is essentially a holistic extension of the “Conventional PL Measurement” technique.[152]

Figure 4.

Stretched Penile Length INdicator Technique

The volume of prepuce is variable between individuals. A large number of studies have specified that the prepuce was not included with the measurement;[12,24,44,95,119] this may not be conveniently possible in participants with physiological (children) or pathological phimosis. Retraction of the prepuce at least enough to expose the tip of the glans (distal landmark) during measurement is necessary. In cases where it is not possible to expose the tip of the glans, the use of another ruler is held perpendicular to the first one and used to press against the prepuce. The volume of the prepuce is much less in children and the final reading proxies the actual measurement closely.

The ruler is the most common device used to measure the PL; the other devices are the flexible tape, conventional or digital vernier calipers, cotton swab, wooden spatulas (tongue depressors), FitKit®, etc. The choice of the measuring device is partly governed by the circumstances of measurement and partly by the convenience of the observer. The device should be lightweight with rounded ends and must not render the patient susceptible to injury in the event of sudden movement by the uncooperative or unanticipating participant.[62] A rigid ruler (or any other measuring device) is easy to handle during measurement by a single observer and compresses the pubic pad of fat effectively. However, a curved penis (chordee) may appear shorter than the actual length[154] with a rigid ruler; a flexible tape scores superior. However, a flexible scale or tape may not be able to compress the fat with its edge, and given its pliable nature, it has the capability of bending and giving an inaccurate reading.

A technique which may be implemented by a single observer is more convenient. One hand may be used to stabilize the penis while the other hand holds the measuring device. The use of flexible tape for measurement of SPL will require a third hand to stretch the tape along the length of the penis.[99,141] The same is true for unmarked wooden spatulas or tongue depressors. An assistant is required to mark the level of the tip of the glans on the spatula while the observer holds the penis in the right hand and the spatula with the left.[11,26,44,129,137]

The Vernier calipers are sturdy and have a bulky head; there is a theoretical possibility of local injury and additional caution is warranted.[62] Besides, the design of the Vernier is not suited to the local anatomy; it may not be possible to compress the prepubic pad of fat with its head.[62] This is in concordance with the findings of the synthesis that the ruler is the most commonly used measuring device (52% of the studies). The other devices have been used less frequently, measuring tape in 15%, wooden spatulas in 11%, and calipers in 10%.

Self-reported measurements are associated with a higher risk of bias related to self-perception, minor variations in technique, state of arousal, and a psychological obligation to exaggerate.[70,106,141] The technique should be such that the subject may take the measurement on his own. The colored measuring strips were not calibrated to encourage honest reporting; instead the participants were asked to mark the penile dimensions on the strip itself with a pen[128] or by creasing it[145] or to tear the paper at the correct point.[141]

The amount of stretching optimal for the measurement of SPL is a topic for further research. The authors encountered multiple suggestions in studies across the cohort. SPL should ideally be measured while the subject is awake and responsive to pain and discomfort.[94,123,146] The limit of stretching may be defined as the point of increased resistance[11,26,51,146] which should correlate with feelings of pain and discomfort. Wessells et al. practice of repeated manual stretching of the penis thrice before actual measurement may help in eliminating muscle inertia and prepare the patient to tolerate the associated discomfort within physiological limits.[142] The use of a syringe and suction for the measurement of SPL may be instrumental in eliminating the subjectivity with manual stretching.[138] A spring scale (450 g) may also be used to ensure uniform stretching across the study group.[93] The amount of force which may be considered optimal for stretching in children will, however, also depend on the age of the patient.

The use of ultrasonography (USG) to measure the SPL has been claimed to be a more accurate representation of functional PL by Smith et al.[144] The USG-estimated SPL has remained fairly constant from 1 week to 22 months of age. The increase in ruler-estimated SPL has been postulated to be due to the growth and elasticity of penile soft tissues and corpus spongiosum rather than specific genital growth.[143] The effect of inconsistent traction is eliminated.[150] USG-guided measurement is likely to be unaffected by body habitus, the presence or absence of preputial skin, or the thickness of pubic pad of fat.[143] It may be ideal for those with phimosis, buried penis, or webbed scrotum.

The EPL during orgasm may be different from that achieved during clinical examination in the presence of an observer or during self-measurement with the mindset of self-measurement. Besides, manual stimulation may not be as effective as actual arousal while pharmacological stimulation may overshoot the physiological routine in a dose-dependent manner. Getting a fully erect length is almost impractical in newborns, infants, and even adult males due to anxiety, apprehension, thermal, tactile, and other environmental factors.[58,144]

The possibility of a parallax error has not been considered in any of the studies across the cohort. To minimize this error, the subject should bend down so that his eyes are aligned with the tip of the glans (highest point of measurement).

The “zero” calibration in most of the rulers starts a couple of millimeters beyond the edge. The same value has to be added to the observed reading to get the actual PL; this factor has not been highlighted in any of the studies.

The synthesis is limited by the quality of information available: (i) the lack of a measuring standard acceptable globally; (ii) the heterogeneity of measuring devices technique and reporting standards; (iii) the limitations imposed by inter-individual variations which could be physiological (such as pubic pad of fat and inherent elasticity of penile tissues) or pathological (such as chordee, phimosis, webbed scrotum or buried penis); and (iv) suboptimal description of the technique or measuring device. The SPLINT modeled herewith may not be ideal for measurement of penises with inherent chordee such as in cases with severe hypospadias or congenital short urethra. Similarly, the measurement may be a close approximation in cases with phimosis where the prepuce may not be retracted enough to expose the tip of the glans.

CONCLUSIONS

A wide range of heterogeneity in the technique used for the estimation of PL has been observed across the studies included in the current review; the factors accounting for this heterogeneity have been identified along with the respective variables and modeled into SPLINT for the measurement of SPL.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.